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The Branner Geological Library 




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CLIMATE AND TIME. 



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V 



Li 



CLIMATE AND TIME 



V& THEIR 



GEOLOGICAL RELATIONS: 



A TltEOET OF 



SECUUR CHANGES OF THE EARTH'S CLIMATE. 



BY 



JAMES CROLL, 

or TXWk MARSTfS OCOLOOZCAL BITBTST 9§ SOOTLAKO. 






. • ■ 
• •• 



* • 






J.it* i>a « • 



NEW YORK: 
D. APPLETON AND COMPANY, 

1, 3, AND 6 BOND STREET. 

1893. 



213283 



PREFACE TO THE FIRST EDITION, 



Ik tlie following pages I have endeayoured to give a full and 
concise statement of the facts and arguments adduced in sup- 
port of the theory of Secular Changes of the Earth's Climate. 
Considerable portions of the volume have already appeared in 
substance as separate papers in the Philosophical Magazine and 
other journals during the past ten or twelve years. The theory, 
especially in as far as it relates to the cause of the glacial epoch, 
appears to be gradually gaining acceptance with geologists. 
This, doubtless, is owing to the greatly increased and con- 
stantly increasing knowledge of the drift-phenomena, which 
has induced the almost general conviction that a climate such 
as that of the glacial epoch could only have resulted from 
cosmical causes. 

Considerable attention has been devoted to objections, and to 
the removal of slight misapprehensions, which have naturally 
arisen in regard to a subject comparatively new and, in many 
respects, complex, and beset with formidable difficulties. 

I have studiously avoided introducing anything of a hypo- 
thetical character. All the conclusions are based either on 
known facts or admitted physical principles. In short, the aim 
oFihe work, aa will be shown in the introductory cha5\«t»V%\ft 



vi PREFA CR 

prove that secular changes of climate follow, as a necessary 
effect, from admitted physical agencies, and that these changes, 
in as far as the past climatic condition of the globe is con 
cemed, fully meet the demand of the geologist. 

The volume, though not intended as a popular treatise, will 
be found, I trust, to be perfectly plain and intelligible even to 
readers not familiar with physical science. 

I avail myself of this opportunity of expressing my obli- 
gations to my colleagues, Mr. James Geikie, Mr. Robert L. 
Jack, Mr. Eobert Etheridge, jun., and also to Mr. James Paton, 
of the Edinburgh Museum of Science and Art, for their valu- 
able assistance rendered while these pages were passing through 
the press. To the kindness of Mr. James Bennie I am in- 
debted for the copious index at the end of the volume, as well 
as for many of the facts relating to the glacial deposits of the 
West of Scotland. 



EDurauROH, March^ 1876 



I 



CONTENTS. 



CHAPTEE I. 

ZKTBODXrOTIOir. 

The Fundamental Problem of Qeolo^. — (^eologjr a Dynamical Soienoe.— 
The Nature of a Geoloffioal Principle. — TheorioB of G^logioal Climate. 
—Geological Climate obpendent on Astronomical Caosea. — An Impor- 
tant Consideration overlooked. — ^Abstract of the Line of Argument pur- 
■ned in the Volume • • • . • . . . • 1 

CHAPTEE n. 

OGBAN-OUBBSNTS IV RBLATIOV TO THE DISTRIBUTION OF HEAT OTZB 

THB OLOBB. 

The abaolute Heating-power of Ooean-ourrents. — ^Volume of the Qulf- 
stream. — ^Absolute Amount of Heat conveyed b^ it. — Greater Portion 
of Moistuxe in Inter^tropioal Begiona falls as Bain in those Begions.— 
Land along the Equator tends to lower the Temperature of the Globe. 
— Influence of Gulf-stream on Climate of Europe. — ^Temperature of 
Space. — ^Badiation of a Particle. — ^Professor Dove on Normal Tem- 
perature. — ^Temperature of Equator and Poles in the Absence of 
Ocean-currents. — Temperature of London, how much due to Ocean- 
currents 28 



CHAPTEB in. 

ocEAN-cu&EEirrs m belatiok to the distbibution of heat oyeb 

THE QjjOBB.'^CotUinued.) 

Influence of the Gulf-stream on the Climate of the Arctic Begions. — Abso- 
lute Amount of Heat received by the Arctic Begions from the Sun.*- 
Influence of Ocean-currents shown by another Method. — ^Temperature 
of a Globe all Water or all Land according to Professor J. D. Forbes. 
— ^An important Consideration overlooked. — Without Ocean-currents 
the Globe would not be habitable. — Conclusions not affected by Imper- 
fection of Data •••••4A 



via CONTENTS. 



CHAPTER IV. 

OUTLINE OF THE FHYSIOAL AOENOIES WHICH LEAD TO SECULAR 

CHANGES OF CLIMATE. 

FAOI 

Eccentricity of the Earth's Orbit ; its Effect on Oiimate. — Glacial Epoch 
not the direct Result of an Increase of Eccentricity. — An important 
Consideration overlooked. — Change of Eccentricity affects Climate only 
indirectly. — Agencies which are brought into Operation by an Increase 
of Eccentricity. — How an Accumulation of Snow is produced. — The 
Effect of Snow on the Summer Temperature. — Reason of the Low 
iSummer Temperature of Polar Regions. — Deflection of Ocean-currents 
the chief Cause of Secular Cbanges of Climate. — How the foregoing 
Causes deflect Ocean-currents. — Nearness of the Sun in Perigee a 
Cause of the Accumulation of Ice. — A remarkable Circumstance re- 
garding the Causes which lead to Secular Changes of Climate. — The 
primary Cause an Increase of Eccentricity. — Mean Temperature of 
whole Earth should be greater in Aphelion than in Perihelion. — Pro- 
fessor Tyndall on tlie Glacial Epoch. — A general Reduction of Tem- 
perature will not produce a Glacial Epoch. — Objection from the present 
Condition of the Planet Mars 64 



CHAPTEE V. 

REASON WHY THE 80UTHEBN HEMTPiPHEBE IS COLDEB THAN THE 

NORTHEBN. 

Adh6mai^8 Explanation. — Adh^mar's Theury founded upon a physical Mis- 
take in regard to Radiation. — Professor J. D. Forbes on Underground 
Temperatare.~-Generally accepted Explanation. — Low Temperature 
of Southern Hemisphere attributed to I*reponderanoe of Sea. — Heat 
transftBrred from Southern to Northern Hemisphere by Ocean-onrrent 
the true Explanation. — A large Portion of the Heat of the Gulf-stream 
derived from the Southern Heminphere • • • • • 81 



CHAPTEE VL 

EXAMINATION OF THE QRAYITATION THEOBY OF OCEANIC CIBCULA« 

TION. — ^LIETJT. MAUBY's THEOBY. 

Introduction. — Ocean-currents, according to Manry, due to Difference of 
Specific Gravity. — Difference of Specific Ghttvity resulting from Dif- 
ference of Temperature. — Difference of Specific Gravity resulting from 
Difference of Saltness. — Maury's two Causes neutralise each ouer. — 
How, according to him, Difference in Saltness acts ai a Cause • • M 



CONTENTS. 



CHAPTER Vn. 

■ZAiairJLTION OF THB O&^TITATIOjr THEOBT OF OCEAKIO CIBCUUk* 

TiOK. — ^LBEXTT. mauby's THEOBT. — (^Continued.) 

Hethods of determinisg the Qaestion. — The Force renilting from DiffereDce 
of Spodfic Giavitj. — Sir John Herschel'i Estimate of the Force. — 
Maximum Density of Sea- Water. — Bate of Decrease of Temperature 
of Ocean at Equator. — The actual Amount of Force retuldng from 
Difference of Specitio Gravity. — M. Dubuat's Experiments . . . 1 16 



CHAPTEE Yin. 

BZAMIKATIOX OF THE OBATITATI027 THEOBY OF OCEANIO CIBCU- 

LATION. — ^DB. GABPENTEB'S THEOBY. 

GhUf-stream according to Dr. Carpenter not due to Difference of Specific 
Gravity. — Facts to be Expluned. — The Explanation of the Facts. — 
The Explanation hjrpothetical. — ^The Cause assigned for the hypo- 
thetical Mode of Circulation. —Under Currents accoimt for all the 
Facts better than the Gravitation Hypothesis. — Known Condition of 
the Ocean inconsistent with that Hypothesis 122 



CHAPTEE IX. 

EXAMINATION OF THE QBAYITATION THEOBY OF OCEAKIO CIBCTJLA- 
TION. — THE 1CECHANIC8 OF DB. GABPEKTEB's THEOBY. 

Kzperimental Illustration of the Theory. — The Force exerted by Gravity. 
— Work performed by Gravity. — Circulation not by Convection. — 
Circulation depends on Difference in Density of the Equatorial and 
Polar Columns. — Absolute Amount of Work which can oe performed 
by Gravity. — How Underflow is produced. — ^How Vertical Descent at 
the Polos and Ascent at the Equator is produced. — The Gibraltar 
Current. — Mistake in Mechanics concerning it. — The Baltic Current . 1411 



CHAPTEE X. 

ATION OF THB OBAVITATION THEOBY OF OGfEAKIC CIBCUUi 
TION. — ^DB. CABPENTEB'b THEOBY.— OBJECTIONS CONSIDERED. 

ModuM Operandi of the Matter. — Polar Cold considered by Dr. Carpenter 
the Frimum Mobile, — Supposed Influence of Heat derived from the 
Earth*e Crust. — Circulation without Difference of Level. — A Confusion 
of Ideas in Reference to the supposed Agency of Polar Cold. — M. 
Dnbuat*s Experiments. — A Begging of the Question at Issue. — 
Plrcssure as a Cause of Circnlatioii 172 



CONTENTS. 

CHAPTER XI. 

THE INADEQUACY OP THE GBAVITATION THEORY PBOVED BY 

ANOTHEB METHOD. 



FAOI 



Quantity of Heat which oan bo conveyed by the General Oceanic Circula- 
tion trifling. — Tendency in the Advocates of the Gravitation Theory to 
under-eetimate the Volume of the Gulf-stream. — Volume of the Stream 
as determined by the Challenger. — Immense Volunte of Warm Water 
discovered by Captain Nares. — Condiiion of North Atlantic incon- 
sistent with the Gravitation Theory. — Dr. Carpenteit^s Estimate ot the 
Thermal Work of the Gulf-stream 191 

CHAPTEE Xn. 

MB. A. G. FINDLAY*S OBJECTIONS CONSIDEBED. 

Mr. Fiiidlay's Estimate of the Volume of the Gulf-stream. — ^Mean Tem- 
perature of a Cro»s Section less than Mean Temperature of Stream. — 
Keason of such Diversity of Opinion regarding Ocean-currents. — More 
rigid Method of Investigation necessary 203 

CHAPTER XTTT. 

THE WIND THEOBY OF OCEANIC CIBCULATION. 

Ocean- Currents not due alone to the Trade-winds. — An Objection by 
Maury. — ^Trade-winds do not explain the Great Antarctic Current. — 
Ocean-currents due to the System of Winds. — The System of Currents 
agrees with the System of the Winds. — Chart showing the Agreement 
between the System of Currents and System of Winds. — Cause of the 
Gibraltar Current. — North Atlantic an immense Whirlpool. — Theory 
of Under Currents. — Difficulty regarding Under Currents obviated. 
— ^Work performed by the Wind in impelling the Water forward. — 
The Challenger^t crucial Test of the Wind ana Gravitation Theories. — 
North Atlantic above the Level of Equator. — Thermal Condition of the 
Southern Ocean irreconcilable with the Gravitation Theory • • 210 

CHAPTER XIV. 

THE WIND THEOBY OF OCEANIC CIBCULATION IN BELATION TO 

CHANGE OF CLIMATE. 

Direction of Currents depends on Direction of the Winds. — Causes which 
affect the Direction of Currents will affect Climate. — How Change of 
Eccentricity affects the Mfide of Distribution of the Winds. — Mutuiil 
Reaction of Caase and Effect. — Displacement of the Great Equatorial 
Current — ^Displacement of the Median Line between the Trades, and 
its Effect on Currents. — Ocean-currents in Relation to the Distribution 
of Plants and Animals. — Alternate Cold and Warm Periods in North 
and South. — Mr. Darwin's Views quoted. — How Glaciers at the 
Equator may be acoonnted for. — Migration across the Equator • . 220 



CONTENTS. 



CHAPTEE XV. 



WABM INTEB-QIACIAL PERIODS. 



MOB 



AHrmate Cold and Warm Periods. — ^Warm Inter-glacial Periods a Test of 
Theories. — Reason why their Occmrencti has not been hitherto recog- 
nised. — Instances of Warm Inter-glacial Periods. — Dmnse, Diirnten, 
Uozne, Chapelhall, Graiglockhart, Leith-Walk, Itedhall Quarry, Beith, 
Crofthead, Kilmaurs, Sweden, Ohio, Cromer, Mundesley, &e., &c. — 
Cave and River Deposits. — Occurrenre of Arctic and Warm Animals 
in seme Beds accounted for. — Mr. Boyd Dawkins's Objections. — Oc- 
currence of Southern Shells in Glacial Deposits. — Evidence of Warm 
Inter-glacial Periods from Mineral Borings. — Striated Pavements. — 
Reason why Inter-glacial Land-surfaces are so rare .... 236 



CHAPTER XVI. 

WAKM DTTEB-GLACIAL FEBIODS IJf ABCTIO BEOIONS. 

Gold Periods best marked in Temperate, and Warm Periods in Arctic, 
Regions. — State of Arctic Regions during GLicial Period. — Effects of 
Removal of Ice from Arctic Regions. — Ocean-curroiits ; Influence on 
Arctic Climate. — Reason why Remains of Inter-glacial Period are rare 
in Arctic Regions. — Remains of Ancient Forests in Banks's Land, 
Prince Patrick's Island, &c. — Opinions of Sir R. Murchison, Captain 
Osbom, and Professor Uaughton.— Tree dug up by Sir E. Belcher in 
lAt. 76<^ N. . 268 



CHAPTER XATE. 

FO&ME& GLACIAL EPOCHS. REASON OF THE IMPERFECTION OF 

GEOLOGICAL RECORDS IN REFERENCE TO THEM. 

Two Reasons why so little is known of Glacial Epochs. — ^Evidence of 
Glaciation to be found on Land-surfaces. — Where are all our ancient 
Land-surfaces P — The stratified Rocks consist of a Series of old Sea- 
bottoms. — Transformation of a Land -surface into a Sea-bottom oblite- 
rates all Traces of Glaciation. — Why so little remains of the Boulder 
Clays of former Glacial Epochs. — Records of the Glacial Epoch are fast 
disappearing. — Icebergs do not striate the Sea-bottom. — Mr. Camp- 
bell's Observationson the Coast of Labrador. — Amount of Material trans- 
ported by Icebergs much exaggerated. — Mr. Packard on the Glacial 
Phenomena of Labrador. — Boulder Clay the Product of LMud-ice. — 
Palsontological Evidence. — Paucity of Life characteristic of a Glacial 
Period. — Warm Periods better represented by Organic Remains than 
cold. — Why the Climate of the Tertiary Period was supposed to be 
warmer than the present. — Mr. James Geikie on the Detects of 
Falvontolofrical Evidence. — Conclusion 266 



wd CONTENTS. 

CHAPTEE XVin. 

FORMER GLACIAL EPOCHS; GEOLOGICAL EYIDENCE OF. 

Cumbrian Conglomerate of Islay and North-west of Scotland. — Ice-action 
in Ayrshire and Wigtownshire during Silurian Period. — Silurian 
Limestontis in Arctic Regions. — Professor Ramsay on Ice-action during 
Old Red Sandstone Period. — Warm Climate in Arctic Regions during 
Old Red Sandstone Period. — Professor Geikie and Mr. James Qeikie 
on a Glacial Conglomerate of Lower Carboniferous Age. — Professor 
Haughton and Professor Dawson on Evidence of Ice-action during 
Coal Period. — Mr. W. T. Blanford on Glaciation in India during 
Carboniferous Period. — Carboniferous Formations of Arctic Regions. 
— Professor Ramsay on Permian Glaciers. — Permian Conglomerate in 
Arran. — Professor Hull on Boulder Clay of Pennian Age. — Permian 
Boulder Clay of Natal. — Oolitic Boulder Conglomerate in Satherland- 
shire. — Warm Climate in North Greenland during Oolitic Period. — 
Mr. God win -Austen on Ice-action during Cretaceous Period. — Glacial 
Conglomerates of Eocene Age in the Alps. — ^M. Gastaldi on the Ice- 
transported Limestone Blocks of the Superga.- -Professor Heer on the 
Climate of North Greenland during Miocene Period .... 293 

CHAPTEE XIX. 

GEOLOGICAL TIME. — PROBABLE DATE OF THE GLACIAL EPOCH. 

Geological Time measurable from Astronomical Data. — M. Levorrier's For- 
mulsB. — ^Tables of Eccentricity for 3,000,000 Years in the Past and 
1,000,000 Years in the Future. — How the Tables have been computed. 
— Why the Glacial Epoch is more recent than had been supposed. — 
Figures convey a very inadequate Conception of immense Duration. — 
Mode of representing a Million of Years. — Probable Date of the 
Glacial Epoch 811 

CHAPTER XX. 

OXOLOGICAL TIME. — METHOD OF MEASTTRrNG THE RATE OF SUBASrIAI 

DENUDATION. 

Bate of Subaerial Denudation a Measure of Time. — Rjite determined from 
Sediment of the Mississippi. — Amount of Sediment carried down by 
the Mississippi ; by the Ganges. — Professor Geikie on Modem Denu- 
dation. — Professor Geikie on the Amount of Sediment conveyed by 
European Rivers. — Rate at which the Surface of the Globe is being 
denuded. — Alfred Tylor on the Sediment of the Mississippi. — ^The 
Law which determines the Rate of Denudation. — ^The Globe becoming 
less oblate. — Carrying Power of our River Systems the true Measure 
of Denudation. — Marine Denudation trifling in comparison to Sub- 
aerial. — ^Previous Methods of measuring Geological Time. — Circum- 
stances which show the recent Date of uo Gflacial Epoch. — Professor 
Ramsay on Geological Time S2I 



CONTENTS. an 

CHAPTER XXL 

THE PBOBABUS AQE Ain> OBIOIN OF THE 6UK. 

FAOI 

GimTitation Theory.— Amount of Heat mnitted bj the San. — Meteorio 
Theory. — Uelmholtz*8 Condensation Theory. — Confunion of Ideus. — 
Gravitation not th^ chief Soarce of the Sun's Heat.— Original lie at. — 
Soorce of Original Heat. — Original Heat derived from Motion in S(>ace« 
— Conclusion as to Date of Glacial £i)och. — Falee Analogy. — Probable 
Date of Eocene and Miocene Periods 846 



CHAPTER XXII. • 

A METHOD OF DETERMDOlfO THE MEAX THICKNESS OF THE 
SEDniEJNTTA&Y BOCKS OF THE QLOBE. 

Prevailing Methods defective. — Maximum Thickness of British Rocks. — 
Three Elements in the Question. — i^rofessor Huxley on the Kate of 
Deposition. — Thickness of Sedimentary Rocks enormously over- 
estimated. — Observed Thickness no Measure of me^m Thickness. — 
Deposition of Sediment principally along Sea-margin. — Mistaken In- 
ference regarding the Absence of a Formation. — Immense Antiquity 
of existing Oceans 860 

CHAPTER XXm. 

THE PHYSICAL CAUSE OF THE SITBMERGENCE AND EMEBOENCE 
OF THE LAND DTJBmO THE GLACIAL EPOCH. 

I>isplaceroent of the Earth's Centre of Gravity by Polar Ice-cap. — Simple 
Method of estimating Amount of Displacement. — Note by Sir \V. 
Thomson on foregoing Methr)d. — Difiference between Continental Ice 
and a Qlacier. — Probable Thickness of the Antarctic Ice-cap. — 
Probable Thickness of Greenland Ice-sheet. — The Icebergs of the 
Southern Ocean. — Inadequate Conceptions regarding the Magnitude 
of Continental Ice 368 



CHAPTER XXIV. 

THE PHYSICAL CAUSE OF THE SXJBMEHGENCE AIO) EMERGENCE OF 
THE LAND DURING THE GLACIAL EPOCH. {Continued,) 

Extent of Submergence from Displacement of Earth's Centre of Gravity. — 
Circumstances which show that the Glacial Submergence resulted from 
Displacement of the Earth's Centre of Gravity. — Agreement between 
Theory and Observed Facts. — Sir Charles Lyell on submerged Areas 
during Tertiary Period. — Oscillations of Sea-Level in Relation to Dis- 
tribution. — Extent of Submergence on the Hypothesis that the Earth 
ia fluid in the Interior 387 



m CONTENTS. 



CHAPTEE XXV. 

THE INFLUENCE OF THE OBLIQTTITT OF THE ECLIPTIO ON CLIMATE 

AND ON THE LEVEL OF THE SEA. 

PAOI 

rhe direct Effect of Change of Obliquity on Climnte. — Mr. Stockwell on 
tbe maximum Change of Ohiiquity. — How Obliquity affects the Dis- 
tribution of Heat over the Globe. — Increase of Obliquity diminishes 
the Heat at the Equator and increases that at the Poles. — Influence of 
Change of Obliquity on the Level of the Sea. — When the Obliquity 
was last at its superior Limit. — Probable Date of the 2d-foot raised 
Beach. — Probable Extent of Rise of Sea-level resulting from Increase 
of Obliquity. — Lieutenant-Colonel Drayson'H and Mr. Belt's Theories. 
— Sir Charles Lyell on Influence of Obliquity 398 



CHAPTEE XXVI. 

COAL AN INTER-GLACIAL FORMATION. 

Climate of Coal Period Inter-glacial in Character. — Coal Plants indicate 
an Equable, not a Tropical Climate. — Conditions necessary for Preser- 
vation of Coal Plants. — Oricillations of Sea-level necessarily implied. — 
Why our Coal-fields contain more than One Coal-seam. — ^Time re- 
quired to form a Bed of Coal. — Why Coal Strata contain so little 
evidence of Ice-action. — Land Flat during Coal Period. — Leading Idea 
of the Theory. — Carboniferous Limestones 420 



CHAPTER XXVn. 

PATH OF THE ICE-SHEET IN NORTH-WESTERN EUROPE AND ITS 
RELATIONS TO THE B0X7LDER CLAY OF CAITHNESS. 

Character of Caithness Boulder Clay. — Theories of the Origin of the Caith- 
ness Clay. — Mr. Jamieson's Theory. — Mr. C. W. Peach's Theory. — 
llie proposed Theory. — Thickness of Scottish Ice-sheet. — Pentlands 
striated on their Sammits. — Scandinavian Ice-sheet. — North Sea filled 
with Land-ice. — Great Baltic Glacier. — Jutland and Denmark crossed 
by Ice. — Sir R. Murchison's Observations. — Orkney, Shetland, and 
Faroe Islands striated across. — Loess accounted for. — Professor Geikie's 
Suggestion. — Professor Geikie and B. N. Peach's Observations on East 
Coast of Caithness. — Evidence from Chalk Flints and Oolitic FossilB in 
Boulder Clay • • • 4I£ 



CONTENTS. xf 



CHAPTER XXVm. 

HOBTH OF ENGLAND ICE-SHEET, AND TBANSPORT OF WASTDALB 

CBAO BLOCKS. 

Traniiport of Blocks ; Theories of. — Evidence of Continental Ice. — Pennine 
liknge probably striated on Summit. — Glacial Drift in Centre of Eng- 
land. — Mr. Lacy on Drift of Cotteswold Hills. — England probably 
crossed by Land-ice. — Mr. Jack's Suggestion. — Shedding of Ice North 
and South. — South of England Ice-sheet. — Glaciation of West Somer- 
set. — ^Why Ice-nuirkings are so rare in South of England. — Form of 
Contortion produced by Land-ice 466 



CHAPTEE XXIX. 

KVJLDJmCE FBOH BURIED RIYEB CHANNELS OF A CONTINENTAL PERIOD 

IN BRITAIN. 

Remarks on the Drift Deposits. — Examination of Drift by Borings. — 
Buried River Cliannel from Kilsyth to Grangemouth. — Channels not 
excavated by Sea nor by Ice. — Section of buried Channel at Grange- 
mouth. — Mr. Milne I^ome's Theory. — German Ocean dry Land. — 
Buried River Channel from Kilsyth to the Clyde. — Journal of Borings. 
— Marine Origin of the Drift Deposits. — Evidence of Inter-glacinl 
Periods. — OscillationB of Sea-Level.— Other buried River Channels . 460 



CHAPTER XXX. 

THB PHYSICAL CAUSE OF THE MOTION OF GLACIERS. — THEORIES 

OF GLACIER-MOTION. 

Why the Question of Glacier -motion has been found to be so difficult. — 
The Regelution Theory. — It accounts for the Continuity of a Glacier, 
but not for its Motion. — Gravitation proved by Canon Moseley insuf- 
ficient to shear the Ice of a Glacier. — Mr. Matthew's Experiment. — 
No Parallel between the bending of an Ice Piank and the shetiring of 
a Glacier. — Mr. Ball's Objection to Canon Moseley's Experiment. — 
Canon Moseley's Meihod of determining the Unit of Shear. — Defect of 
Method. — Motion of a Glacier in some Way dependent on Heat. — 
Canon Moseley's Thiory. — Olijoctions to hisTheoiy. — Professor James 
Thomson's Theory. — This Theory fails to explain Glacier-motion. — De 
Saussure and Hopkins's ** Sliding" Theories. — M. Charpentier's "Dila- 
tatioa" Theory.— Important Element in the Theory . • • • 495 



xn CONTENTS. 



CHAPTEB XXXI. 



THE PHYSICAL CAUSE OF THE MOTION OF OLACIEBS. — THE 

HOLECULAB THEOBY. 



FAOI 



Present State of the Question.— Heat necessary to the Motion of a Glacier. 
— Ice does not shear in the Solid State. — Motion of a Glacier molecular. 
— How Heat is transmitted through Ice. — Momentary Loss of Shear- 
ing Force. — The Nationals of Resrelation. — The 0rigi4 of ** Cre- 
vasses." — Effects of Tension. — Modification of Theory. — Fluid Mole- 
cules crystallise in Interstices. — Expansive Force of crystallizing 
Molecules a Cause of Motion. — Internal molecular Pressure the chi^ 
Moving Power. — How Ice can excavate a Rock Basin. — How Ice can 
ascend a Slope. — How deep River Valleys are striated across. — A 
remarkable Example in the Valley of the Tay. — How Boulders can be 
carried from a lower to a higher Level 614 



APPENDIX. 

I. Opinions expressed previous to 1864 refcsrding the Influence of the 

Eccentricity of the Earth's Orbit on Climate .... 628 

II. On the Nature of Heat- Vibrations 646 

III. On the Reason why the Difference of Reading between a Thermo- 
meter exposed to direct Sunshine and One Shaded diminishes as we 
ascend in the Atmosphere 648 

IV. Remarks on Mr. J. Y. Buchanan's Theory of the Vertical Distribu- 
tion of Temperature of the Ocean 662 

V. On the Cause of the Cooling Effect produced on Solids by Tension. 664 

VI. The Cause of Regelation 666 

VII. List of Papers which have appeared in Dr. A. Petermann's Oeo- 
graphische Mittkeilungm relating to the Gulf-stream and Thermal 
Condition of the Arctic Regions 658 

VIII. List of Papers by the Author to which Reference is made in this 

Volume 662 



tlTDBZ ••••. 561 



LIST OF PLATES. 



EIabth's Qsbit ween Eogentbicitt is at its Superior 

XiDfiT Fronti9pue$, 

L Showino Aokeemznt between the System of Oceak- 

CuBSENTS AiTD WnTOS . . . To foce pag$ 212 

II. Showing how opposing Citrrents intersect eaoh 

other ......... 219 

m. Section of Mid-Atlantio 222 

lY. DiAGBAH BEFBESSNTING THE VARIATIONS OF ECCEN- 

TRIdTT OF THB EARTH'S OrBIT 313 

Y. Showing probable Path of the Iob in North- 

Wbstebn Extbopb 449 

yi. Showing Path of Ice acboss Caithness . . • 453 

VXE. Map of the Midland Yallet (Scotland), showing 

bubied Biyeb Channels 471 



i 



::iTr*:r • * 









CHAPTER I. 

INTRODUCTION. '"".* 



The Fundamental Problem of Oeology. — Geology a Dynamical Scieiice.Vv*^« 
l^ature of a Geological Principle. — ^Theories of Oeological Climate.-rG$i9- 
loffical Climate dependent on Astronomical Cauaes.— An Important O^ 
■ideration OYerlooked. — ^Abstract of the Line of Argument pursued inthA 
Volume. 

The Fundamental Probkm of Oeology. — The inyestigation of 
the succesaive changes and modifications which the earth's 
crust has undergone daring past ages is the province of geology. 
It will be at once admitted that an acquaintance with the 
agencies by means of which those successive changes and modi- 
fications were efiected, is of paramount importance to the 
geologist. What, then, are those agencies P Although volcanic 
and other subterranean eruptions, earthquakes, upheavals, and 
subsidences of the land have taken place in all ages, yet no 
truth is now better established than that it is not by these 
convulsions and cataclysms of nature that those great changes 
were efiected. It was rather by the ordinary agencies that we 
see every day at work around us, such as rain, rivers, heat and 
cold, frost and snow. The valleys were not produced by violent 
dislocations, nor the hills by sudden upheavals, but were actually 
carved out of the solid rock, silently and gently, by the agencies 
to which we have referred. " The tools," to quote the words 
of Professor Geikie, " by which this great work has been done 
are of the simplest and most every-day order — the air, rain, 
frosts, springs, brooks, rivers, glaciers, icebergs, and the sea. 
These tools have been at work from the earliest times of which 
any geological record has been preserved. Indeed, it is out of 



t eiilMATE AND TIME. 

the accumulated *c]}i]^ and dust which they have made, after- 
wards hardened into solid rock and upheaved, that the very 
framework of x)up continents has been formed." * 

It will be^observed — and this is the point requiring particular 
attention— rpHtt the agencies referred to are the ordinary meteoro- 
logical .gr climatic agencies. In fact, it is these agencies which 
constitute '.climate. The various peculiarities or modifications 
of cliln^'^* result from a preponderance of one or more of these 
agenQied over the rest. When heat, for example, predominates, 
we ^i«re a hot or tropical climate. When cold and frost pre- 
doimnate, wo have a rigorous or arctic climate. With moisture 
. *ia' excess, we have a damp and rainy climate ; and so on. But 
• •*t]iis is not all. These climatic agencies are not only the factors 
which carved out the rocky face of the globe into hill and dale, and 
spread over the whole a mantle of soil ; but by them are deter- 
mined the character of the^ora and /auna which exist on that 
soil. The flora and fauna of a district are determined mainly 
by the character of the climate, and not by the nature of the 
soil, or the conformation of the ground. It is from difference 
of climate that tropical life differs so much from arctic, and 
both these from the life of temperate regions. It is climate, and 
climate alone, that causes the orange and the vine to blossom, 
and the olive to flourish, in the south, but denies them to the 
north, of Europe. It is climate, and climate alone, that enables 
the forest tree to grow on the plain, but not on the mountain 
top ; that causes wheat and barley to flourish on the mainland 
of Scotland, but not on the steppes of Siberia. 

Again, if we compare flat countries with mountainous, high- 
lands with lowlands, or islands with continents, we shall find 
that diff^renre of climatic conditions is the chief reason why life 
in the one differs so much from life in the other. And if we turn 
to the sea we find that organic life is there as much under the 
domain of climate as on the land, only the conditions are much 
less complex. For in the case of the sea, difference in the tem- 
perature of the water may be said to constitute almost the only 

« Trans, of Edin. Gool. Soc., toL ii. p. 252. 



INTRODUCTION. 5 

difference of climatic conditions. If there is one &ct more clearly 
bronght oat than another by the recent deep-sea explorations, 
it is thisy that nothing exercises so much influence on organic 
life in the ocean as the temperature of the water. In fact, so 
much is this the case, that warm zones were found to be almost 
equivalent to zones of life. It was found that even the enor- 
mous pressure at the bottom of the ocean does not exercise so 
much influence on life as the temperature of the water. There 
are few, I presume, who reflect on the subject that will not 
readily admit that, whether as regards the great physical 
changes which are taking place on the surface of our globe, or 
as regards the growth and distribution of plant and animal life, 
the ordinary climatic agents are the real agents at work, and 
that, compared with them, all other agencies sink into insigni- 
ficance. 

It will also be admitted that what holds true of the present 
holds equally true of the past. Climatic agents are not only 
now the most important and influential; they have been so 
during all past geological ages. They were so during the 
Cainozoic as much as during the present; and there is no 
reason for supposing they were otherwise during the remoter 
Mesozoic and Fakeozoic epochs. They have been the principal 
factors concerned in tJiat long succession of events and changes 
which have taken place since the time of the solidification of 
the earth's crust. The stratified rocks of the globe contain all 
the records which now remain of their action, and it is the 
special duty of the geologist to investigate and read those 
records. It will be at once admitted that in order to a proper 
imderstanding of the events embodied in these records, an 
acquaintance with the agencies by which tliey were produced 
is of the utmost importance. In fact, it is only by this meanp 
that we can hope to arrive at their rational explanation. A 
knowledge of the agents, and of the laws of their operations, is, 
in all the physical sciences, the means by which we arrive at a 
rational comprehension of the effects produced. If we have 
before us some complex and intricate effects which have been 



4 CLIMATE AND TIME. 

produced by heat, or by light, or by electricity, &c., in order 
to understand them we must make ourselves acquainted with 
the agents by which they were produced and the laws of their 
action. If the effects to be considered be, for example, those 
of heat, then we must make ourselves acquainted with this 
agent and its laws. If they be of electricity, then a knowledge 
of electricity and its laws becomes requisite. 

This is no mere arbitrary mode of procedure which may be 
adopted in one science and rejected in another. It is in reality 
a necessity of thought arising out of the very constitution of 
our intellect ; for the objective law of the agent is the concep- 
tion by means of which the effects are subjectively imited in a 
rational unity. We may describe, arrange, and classify the 
effects as we may, but without a knowledge of the laws of the 
agent we can have no rational unity. We have not got the 
higher conception by which they can be comprehended. It is 
this relationship between the effects and the laws of the agent, a 
knowledge of which really constitutes a science. We might 
examine, arrange, and describe for a thousand years the effects 
produced by heat, and still we should have no science of heat 
imless we had a knowledge of the laws of that agent. The effects 
would never be seen to be necessarily connected with anything 
known to us; we could not connect them with any rational 
principle from which they could be deduced ^ prion. The 
same remarks hold, of course, equally true of all sciences, in 
which the things to be considered stand in the relationship of 
cause and effect. Geology is no exception. It is not like 
systematic botany, a mere science of classification. It has to 
explain and account for effects produced ; and these effects can 
no more be explained without a knowledge of the laws of the 
agents which produced them, than can the effects of heat with- 
out a knowledge of the laws of heat. The only distinction 
between geology and heat, light, electricity, &c., is, that in 
geology the effects to be explained have almost all occurred 
already, whereas in these other sciences effects actually taking 
place have to be explained. But this distinction is of no 



INTRODUCTION. $ 

importance to our present purpose, for effects which have 
already occnrred can no more be explained without a knowledge 
of the laws of the agent which produced them than can effects 
which are in the act of occurring. It is, moreover, not strictly 
trae that all the effects to be explained by the geologist are 
already past. It falls within the scope of his science to account 
for the changes which are at present taking place on the earth's 
crust. 

"So amount of description, arrangement, and classification, how- 
ever perfect or accurate, of the facts which come under the eye of 
the geologist can ever constitute a science of geology any more 
than a description and classification of the effects of heat could 
constitute a science of heat. This will, no doubt, be admitted 
by every one who reflects upon the subject, and it will be main- 
tained that geology, like every other science, must possess 
principles applicable to the facts. But here confusion and 
misconception will arise imless there be distinct and definite 
ideas as to what ought to constitute a geological principle. It 
is not every statement or rule that may apply to a great many 
fisusts, which will constitute a geological principle. A geological 
principle must bear the same characteristics as the principles of 
those sciences to which we have referred. What, then, is the 
nature of the principles of light, heat, electricity, &c. P The 
principles of heat are the laws of heat. The principles of elec- 
tricity are the laws of electricity. And these laws are nothing 
more nor less than the ways according to which these agents 
produce their effects. The principles of geology are therefore 
the laws of geology. But the laws of geology must be simply 
the laws of the geological agents, or, in other words, the 
methods by which they produce their effects. Any other so- 
called principle can be nothing more than an empirical rule, 
adopted for convenience. Possessing no rationality in itself, it 
cannot be justly regarded as a principle. In order to rationality 
the principle must be either resolvable into, or logically deducible 
from, the laws of the agents. Unless it possess this quality we 
cannot give the explanation d priori. 



6 CLIMATE AND TIME. 

The reason of all this is perfectly obvious. The things to be 
explained are effects ; and the relationship between cause and 
effect affords the subjective connection between the principle 
and the explanation. The explanation follows from the principle 
simply as the effect results from the laws of the agent or cause. 

Theories of Geological Climate. — ^We have already seen that 
the geological agents are chiefly the ordinary climatic agents. 
Consequently, the main principles of geology must be the laws 
of the climatic agents, or some logical deductions from them. 
It therefore follows that, in order to a purely scientific geology, the 
grand problem must be one of geological climate. It is through 
geological climate that we can hope to arrive ultimately at 
principles which will afford a rational explanation of the miilti- 
farious facts which have been accumulating during the past 
century. The facts of geology are as essential to the establish- 
ment of the principles, as the facts of heat, light, and electricity are 
essential to the establishment of the principles of these sciences. 
A theory of geological climate devised without reference to the 
facts would be about as worthless as a theory of heat or of elec- 
tricity devised without reference to the facts of these sciences. 

It has all along been an admitted opinion among geologists 
that the climatic condition of our globe has not, during past 
ages, been uniformly the same as at present. For a long time 
it was supposed that during the Cambrian, Silurian, and other 
early geological periods, the climate of our globe was much 
hotter than now, and that ever since it has been gradually 
becoming cooler. And this high temperature of PalflBOzoic ages 
was generally referred to the influence of the earth's internal 
heat. It has, however, been proved by Sir William Thomson* 
that the general climate of our globe could not have been 
sensibly affected by internal heat at any time more than ten 
thousand years after the commencement of the solidification of 
the surface. This physicist has proved that the present in- 
fluence of internal heat on the temperature amounts to about 
only l-75th of a degree. Not only is the theory of internal 

• FhiL Mag., Janaary, ISSa. 



INTRODUCTION. 7 

heat now generally abandoned, but it is admitted that we have 
no good geological eridence tbat climate was much hotter 
during Pabeozoio ages than now ; and much less, that it has 
been becoming umfomUy colder. 

The groat discovery of the glacial epoch, and more lately 
that of a mild and temperate condition of climate extendin^c 
daring the Miocene and other periods to North Gh*eenland» 
have introduced a ccnnplete revolution of ideas in reference to 
gecdogical climate. Those discoveries showed that our globe 
has not only undergone changes of climate, but changes of the 
most extraordinary character. They showed that at one time 
not only an arctic condition of climate prevailed in our island, 
but that the greater part of the temperate region down to com- 
paratively low latitudes was buried under ice^ while at other 
periods Greenland and the Arctic regions, probably up to the 
North Pole, wore not only free from ice, but were covered with 
a rich and luxuriant v^;etation. 

To account for these extraordinary changes of climate has 
generally been regarded as the most difficult and perplexing 
problem which has &llen to the lot of the geologist. Some 
have attempted to explain them by assuming a displacement 
of the earth's axis of rotation in consequence of the uprising of 
large mountain masses on some part of the earth's surface. 
But it has been shown by Professor Airy,* Sir William 
Thomson,! and others, that the earth's equatorial protuberance 
is such that no geological change on its surface could ever 
possibly alter the position of the axis of rotation to an extent 
which could at all sensibly affect climate. Others, again, have 
tried to explain the change of climate by supposing, with 
Poisson, that the earth during its past geological history may 
have passed through hotter and colder parts of space. This is 
not a very satisfactory hypothesis. There is no doubt a dif- 
ference in the quantity of force in the form of heat passing 
through different parts of space ; but space itself is not a sub* 

* Athenmum, September 22, 1860. 

t Trans. Glasgow Oeol. 60c., voL iv., p. 818^ 

2 



8 CLIMATE AND TIME. 

stance which can possibly be either cold or hot. If, therefore, 
we were to adopt this hypothesis, we must assume that the 
earth during the hot periods must have been in the vicinity of 
some other great source of heat and light besides the sun. But 
the proximity of a mass of such magnitude as would be suffi- 
cient to affect to any great extent the earth's climate would, 
by its gravity, seriously disarrange the mechanism of our 
solar system. Consequently, if our solar system had ever, 
during any former period of its history, really come into the 
vicinity of such a mass, the orbits of the planets ought at the 
present day to afford some evidence of it. But again, in order 
to account for a cold period, such as the glacial epoch, we have 
to assume that the earth must have come into the vicinity of a 
cold body.* But recent discoveries in regard to inter-glacial 
periods are wholly irreconcilable with this theory. 

A change in the obliquity of the ecliptic has frequently been, 
and still is, appealed to as an explanation of geological climate. 
This theory appears, however, to be beset by a twofold objection ; 
(1), it can be shown from celestial mechanics, that the varia- 
tions in the obliquity of the ecliptic must always have been so 
small that they could not materially affect the climatic condi- 
tion of the globe ; and (2), even admitting that the obliquity 
coiild change to an indefinite extent, it can be shown f that no 
increase or decrease, however great, coiild possibly account for 
either the glacial epoch or a warm temperate condition of climate 
in polar regions. 

The theory that the sun is a variable star, and that the 
glacial epochs of the geologists may correspond to periods of 
decrease in the sun's heat, has lately been advanced. This 
theory is also open to two objections : (1), a general diminution 
of heat X never could produce a glacial epoch ; and (2), even if 
it could, it would not explain interglacial periods. 

The only other theory on the subject worthy of notice is that 

* See Mr. Hopkin's remarks on this theory, Quart. Joum. Geol. Soc, ?oL Tiii. 
t See Chap. xxv. 
{ See Chap. iv. 



INTRODUCTION, 9 

of Sir Charles Ljell. Those extraordinary changes of climate 
are, according to his theory, attributed to differences in the 
distribution of land and water. Sir Charles concludes that, 
were the land all collected round the poles, while the equatorial 
zones were occupied by the ocean, the general temperature 
would be lowered to an extent that would account for the glacial 
epoch. And, on the other hand, were the land all collected 
along the equator, while the polar regions were covered with 
sea, this would raise the temperature of the globe to an enor- 
mous extent. It will be shown in subsequent chapters that 
this theory does not diily take into account the prodigious 
influence exerted on climate by means of the heat conveyed from 
equatorial to temperate and polar regions by means of ocean 
currents. In Chapters II. and III. I have endeavoured to 
prove (1), that were it not for the heat conveyed from equatorial 
to temperate and polar regions by this means, the thermal 
condition of the globe would be totally different from what it is 
at present ; and (2), that the effect of placing all the land along 
the equator would be diametrically the opposite of that which 
Sir Charles supposes. 

But supposing that difference in the distribution of land and 
water would produce the effects attributed to it, nevertheless it 
would not account for those extraordinary changes of climate 
which have occurred during geological epochs. Take, for 
example, the glacial epoch. Geologists almost all agree that 
little or no change has taken place in the relative distribution 
of sea and land since that epoch. All our main continents and 
islands not only existed then as they do now, but every year is 
adding to the amount of evidence which goes to show that so 
recent, geologically considered, is the glacial epoch that the 
very contour of the surface was pretty much the same then as 
it is at the present day. But this is not all ; for even should 
we assume (1), that a difference in the distribution of sea and 
land would produce the effects referred to, and (2), that wo had 
good geological evidence to show that at a very recent period a 
form of distribution existed which would produce the necessary 



lo CLIMATE AND TIME. 

glacial conditions, still the glacial epoch would not be explained, 
for the phenomena of warm inter-glacial periods would com* 
pletely upset the theory. 

. Oeological Climate depending on Astronomical Causes. — For a 
good m'^my years past an impression has been gradually gaining 
ground amongst geologists that the glacial epoch, as well as the 
extraordinary condition of climate which prevailed in arctio 
regions during the Miocene and other periods, must some way 
or other have resiilted from a cosmical cause ; but all seemed at 
a loss to conjecture what that cause could possibly be. It was 
apparent that the cosmical cause must be sought for in the 
relations of our earth to the sun ; but a change in the obliquity 
of the ecliptic and the eccentricity of the earth's orbit are the 
only changes from which any sensible effect on climate could 
possibly be expected to result. It was shown, however, by 
Laplace that the change of obliquity was confined within so 
iiarrow limits that it has scarcely ever been appealed to as a 
cause seriously afiecting climate. The only remaining cause 
to which appeal could be made was the change in the eccen- 
tricity of the earth's orbit — precession of the equinoxes without 
eccentricity producing, of course, no efiect whatever on climate. 
Upwards of forty years ago Sir John Herschel and a few other 
astronomers directed their attention to the consideration of this 
cause, but the residt arrived at was adverse to the supposition 
that change of eccentricity could greatly affect the climate of 
our globe. 

As some misapprehension seems to prevail with reference to 
this, I woiild take the liberty of briefly adverting to the history 
of the matter, — referring the reader to the Appendix for fuller 
details. 

About the beginning of the century some writers attributed 
the lower temperature of the southern hemisphere to the fact 
that the sun remains about seven days less on that hemisphere 
than on the northern ; their view being that the southern hemi- 
sphere on this account receives seven days less heat than the 
northern. Sir Charles Lyell, in the first edition of his ** Prin- 



INTRODUCTION. ii 

ciplesy'' published in 1830, refers to this as a cause which might 
produce some slight effect on climate. Sir Charles's remarks 
seem to have directed Sir John Herschel's attention to the 
subject, for in the latter part of the same year he read a paper 
before the Geological Society on the astronomical causes which 
may influence geological phenomena, in which, after pointing 
out the mistake into which Sir Charles had been led in con- 
cluding that the southern hemisphere receives less heat than 
the northern, he considers the question as to whether geological 
climate could be influenced by changes in the eccentricity of 
the earth's orbit. He did not appear at the time to have been 
aware of the conclusions arrived at by Lagrange regarding the 
superior limit of the eccentricity of the earth's orbit ; but he 
came to the conclusion that possibly the climate of our globe 
may have been affected by variations in the eccentricity of its 
orbit. "An amount of variation," he says, ''which we need 
not hesitate to admit (at least provisionally) as a possible one, 
may be productive of considerable diversity of climate, and 
may operate during great periods of time either to mitigate or 
to exaggerate the difference of winter and summer tempera- 
tnreSf so as to produce alternately in the same latitude of either 
hemisphere a perpetual spring, or the extreme vicissitudes of a 
burning summer and a rigorous winter." 

This opinion, however, was unfortunately to a great extent 
nullified by the statement which shortly afterwards appeared in 
Us " Treatise on Astronomy/' and also in the '' Outlines of 
Astronomy/' to the effect that the elliptic form of the earth's 
orbit has but a very trifling influence in producing variation of 
temperature corresponding to the sun's distance ; the reason 
being that whatever may be the ellipticity of the orbit, it follows 
that equal amounts of heat are received from the sun in passing 
over equal angles round it, in whatever part of the ellipse those 
angles may be situated. Those angles will of course be de- 
scribed in unequal times, but the greater proximity of the sun 
exactly compensates for the more rapid description, and thus an 
equilibrium of heat is maintained. The sun, for example, is 



II CLIMATE AND TIME. 

much nearer the earth when he is oyer the southern hemi- 
sphere than he is when over the northern ; but the southern 
hemisphere does not on this account receive more heat than the 
northern ; for, owing to the greater Telocity of the earth when 
nearest the sun, the sun does not remain so long on the southern 
hemisphere as he does on the northern. These two effects so 
exactly counterbalance each other that, whatever be the extent 
of the eccentricity, the total amount of heat reaching both 
hemispheres is the same. And he considered that this beautiful 
compensating principle would protect the climate of our globe 
from being seriously affected by an increase in the eccentricity 
of its orbit, unless the extent of that increase was very great. 

" Were it not," he says, ** for this, the eccentricity of the 
orbit would materially influence the transition of seasons. The 
fluctuation of distance amounts to nearly l-30th of its mean 
quantity, and consequently the fluctuation in the sun's direct 
heating power to double this, or l-15th of the whole. Now 
the perihelion of the orbit is situated nearly at the place of 
the northern winter solstice ; so that, were it not for the com- 
pensation we have just described, the effect would be to exag- 
gerate the difference of summer and winter in the southern 
hemisphere, and to moderate it in the northern; thus pro- 
ducing a more violent alternation of climate in the one hemi- 
sphere, and an approach to perpetual spring in the other. As 
it is, however, no such inequality subsists, but an equal and 
impartial distribution of heat and light is accorded to both." ♦ 

Herschel's opinion was shortly afterwards adopted and advo 
cated by Aragof and by Humboldt.j: 

Arag^, for example, states that so little is the climate of our 
globe affected by the eccentricity of its orbit, that even were 
the orbit to become as eccentric as that of the planet Pallas 
(that is, as great as 0*24), " still this would not alter in 

• **Tr«itiBe on Aitronomy," { 316; " Outline*," { 368. 
t Annuaire for 1834, p. 199. Edin. New Phil. Joum., April, 1834, p. 224. 
t ''Cosmos," ToL iv. p. 459 (Bohn's Edition). *< Physical Description of th« 
Heavens," p. 336. 



INTRODUCTION. ij 

any appreciable manner the mean thermometrical state of the 
globe." 

This idea, supported by these great authorities, got posses- 
sion of the public mind ; and ever since it has been ahnost 
uniyersally regarded as settled that the great changes of climate 
indicated by geological phenomena could not have resulted 
from any change in the relation of the earth to the sun. 

There is, however, one effect that was not regarded as com- 
pensated. The total amount of heat received by the earth is 
inversely proportional to the minor axis of its orbit ; and it 
follows, therefore, that the greater the eccentricity, the greater 
is the total amount of heat received by the earth. On this 
account it was concluded that an increase of eccentricity would 
tend to a certain extent to produce a warmer climate. 

All those conclusions to which I refer, arrived at by astro- 
nomers, are perfectly legitimate so far as the direct effects of 
eccentricity are concerned ; and it was quite natural, and, in 
fact, proper to conclude that there was nothing in the mere 
increase of eccentricity that could produce a glacial epoch. 
How unnatural would it have been to have concluded that an 
increase in the quantity of heat received from the sun should 
lower the temperature, and cover the country with snow and 
ice I Neither would excessively cold winters, followed by 
excessively hot summers, produce a glacial epoch. To assert, 
therefore, that the purely astronomical causes coidd produce 
such an effect would be simply absurd. 

Important Cwi^derabum overlooked. — The important &ct, how- 
ever, was overlooked that, although the glacial epoch coiild not 
result directly from an increase of eccentricity, it might never- 
theless do so indirectly. Although an increase of eccentricity 
could have no direct tendency to lower the temperature and 
cover our country with ice, yet it might bring into operation 
physical agents which would produce this effect. 

If, instead of endeavouring to trace a direct connection 
between a high condition of eccentricity and a glacial condition 
of climate, we turn our attention to the consideration of what 



44 CLIMATE AND TIME, 

are tLo pliysicul offeota which resiilt £rom an increase of eoeen- 
trioity, wo shall find that a host of physical agencies are brought 
into operation, the combined effect of which is to lower to a 
Yory groat extent the temperature of the hemisphere whoee 
winters occur in aphelion, and to raise to nearly as great an 
extent the temperature of the opposite hemisphere, whoee 
winters of course occur in perihelion. Until attention was 
directed to those physical circumstances to which I refer, it 
woa impossible that the true cause of the glacial epoch 
Qould have been discovered ; and, moreover, many of the in- 
direct and physical effects, which in reality were those that 
brought about the glacial epoch, could not, in the nature of 
things, have boon known previously to recent discoveries in the 
science of ho^U^ 

The consideration and discussion of those various physical 
igi^nciea are the chief aim of the following pages. 

Ai^imei *if tM^ ZiW o/ ArytufteHt punued ij» tkU Volume. — I 
shall now priKved to give a brief abstract of the line of argu- 
ui«ttt pursued in this volume. But as a considerable portion 
\4' it is dewted to the con^deration of objections and difficultiea 
bctiuring either dirvctly or indiivotly on the theory, it will be 
iiece^HiirT to point out what those difficulties are, how they 
an.v!i\ and the methods which have been adopted to overcome 

Chapter IV. contains an outline of the phy>sieal agenciea 
aftev'tiu^ climatic which are bn>u^ht into opeiatiaa by an in- 
CMase %.^ t^xecLtrkitT. By £iur the mosi impoirtant of all dioae 
a^peociiMiw asid th^ e^e which nuinly brought about the glacial 
epiii^ v^ t^f^ IkritiXim of iVeon Currents The CKMuideimtiQn 
g|* iW iashSii^Kt phy^sacal vvanection Ke^w^en a hi^ ststa «f 
<M<iMi.t7ic£:y awL tb^ d<(&vc^.>a of coeiin ccriects^ aai aljo thm 
<^Mijini iadkfc^ttcvf en clisu^te whxh n»ulta ttvca thia dedee- 
IMfc iXHt^::!)!^ 3C( <iilj th< aK«$5 imj^Nrtaat part of t2ie ■dfa)«cc» 
Whi ^ «i<ae i«Hvt w£:^ :^ ^:tryi&»«6 asbxi:;; cc ii£c;2l:ie«L 

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ife »4pme<c saaae %?£ cor iL3!«»«I<c^«. ^I^' wi;^ iv&ci 



INTRODUCTION. 15 

to the absolute amount of heat transferred from equatorial to 
temperate and polar regions by means of ocean currents and 
die influence wbicb the heat thus transferred has on the distri- 
bution of temperature on the earth's surface ; and (2nd) in con- 
neetion with the physical cause of ocean circulation. 

In Chapters II. and III. I have entered at considerable 
length into the consideration of the effects of ocean currents on 
the distribution of heat over the globe. The only current of 
which anything like an accurate estimate of volume and 
temperature has been made is the Oulf-stream. In refer- 
ence to this stream we have a means of determining in abso- 
lute measure the quantity of heat conveyed by it. On the 
necessary computation being made, it is found that the 
amount transferred by the Gulf-stream from equatorial regions 
into the North Atlantic is enormously greater than was ever 
anticipated, amounting to no less than one-fifth part of the 
entire heat possessed by the North Atlantic. This striking 
£act casts a new light on the question of the distribution of 
heat over the globe. It will be seen that to such an extent is 
the temperature of the equatorial regions lowered, and that of 
high temperate, and polar regions raised, by means of ocean 
ciirrentSy that were they to cease, and each latitude to depend 
solely on the heat received directly from the sun, only a very 
small portion of the globe would be habitable by the present 
order of b^ngs. This being the case, it becomes obvious to 
what an extent the deflection of ocean currents must affect 
temperature. For example, were the Gulf-stream stopped, and 
the heat conveyed by it deflected into the Southern Ocean, how 
enormously would this tend to lower the temperature of the 
northern hemisphere, and raise the temperature south of the 
equator. 

Chapters VI., VII., VIII., IX., X., and XIII., are devoted 
io the consideration of the physical cause of oceanic circulation. 
This has been found to be the most difficult and perplexing 
part of the whole inquiry. The difficulties mainly arise from 
the great diversity of opinion and confusion of ideas prevailing 



1 6 CLIMATE AND TIME. 

in regard to the mechanics of the subject. There are two 
theories propounded to account for oceanic circulation ; the one 
which may be called the Wind theory, and the other the Oravi* 
tation theory ; and this diversity of opinion and confusion of 
ideas prevail in connection with both theories. As the question 
of the cause of oceanic circulation has not only a direct and 
important bearing on the subject of the present volume, but in 
further one of much general interest, I have ent<)red some- 
what fully into the matter. 

The Gravitation theories may be divided into two classes. 
The first of these attributes the Gulf-stream and other sensible 
currents of the ocean to difference of specific gravity, resulting 
from difference of temperature between the sea in equatorial 
and polar regions. The leading advocate of this theory was 
the lute Lieutenant Maury, who brought it so much into pro- 
minence in his interesting book on the " Physical Geography 
of the Sea." The other class does not admit that the sensible 
currents of the ocean can be produced by difference of specific 
gravity ; but they maintain that difference of temperature 
between the sea in equatorial and polar regions produces a 
general movement of the upper portion of the sea from the 
equator to the poles, and a counter-movement of the under 
portion from the poles to the equator. This form of the gravi- 
tation theory has been ably and zealously advocated by Dr. 
Carpenter, who may be regarded as its representative. The 
Wind theories also divide into two classes. According to the 
one ocean currents are caused and maintain-ed by the impulse 
of the trade- winds, while according to the other they are due 
not to the impulse of the trade- winds alone, but to that of the 
prevailing winds of the globe, regarded as a general system. 
The former of these is the one generally accepted ; the latter 
is that advocated in the present volume. 

The relations which these theories bear to the question of 
secidar change of climate, will be found stated at length in 
Chapter VI. It will, however, be better to state here in a few 
words what those relations are. When the eccentricity of the 



INTRODUCTION. 17 

earth's orbit attaiiiB a high Talue, the hemiaphere^ whose winter 
flolstioe occurs in aphelion, has, for reasons which are explained 
in Chapter lY., its temperature lowered, while that of the 
opposite hemisphere is raised. Let us suppose the northern 
hemisphere to be the cold one, and the southern the warm one. 
The difference of temperature . between the equator and the 
Korth Pole will then be greater than between the equator and 
the South Pole ; according, therefore, to theory, the trades of 
the northern hemisphere will be stronger than those of the 
southern, and will consequently blow across the equator to 
some distance on the southern hemisphere. This state of things 
will tend to deflect equatorial currents southwards, impelling 
the warm water of the equatorial regions more into the southern 
or warm hemisphere than into the northern or cold hemisphere. 
The tendency of all this will be to exaggerate the difference of 
temperature already existing between the two hemispheres. If, 
on the other hand, the great ocean currents which convey the 
warm equatorial waters to temperate and polar regions be not 
produced by the impulse of the winds, but by difference of 
temperature, as Maury maintains, then in the case above 
supposed the equatorial waters would be deflected more into 
the northern or cold hemisphere than into the southern 
or warm hemisphere, because the difference of temperature 
between the equator and the poles would be greater on the 
cold than on the warm hemisphere. This, of course, would 
tend to neutralize or counteract that difference of temperature 
between the two hemispheres which had been previously pro- 
duced by eccentricity. In short, this theory of circulation 
would effectually prevent eccentricity from seriously affecting 
climate. 

Chapters VI. and VII. have been devoted to an examination 
of this form of the gravitation theory. 

The above remarks apply equally to Dr. Carpenter's form of 
the theory ; for according to a doctrine of General Oceanic Circu- 
lation resulting from difference of specific gravity between the 
water at the equator and at the poles, the equatorial water will 



1 8 CLIMATE AND TIME. 

be carried more to the cold than to the warm hemisphere. It 
ifl perfectly true that a belief in a general oceanic oirculatioii 
may be held quite consistently with the theory of secular 
changes of climate, provided it be admitted that not this general 
circulation but ocean currents are the great agency employed 
in distributing heat over the globe. The advocates <^ the 
theory, however, admit no such thing, but regard ocean currents 
as of secondary importance. It may be stated that the existence 
of this general ocean circulation has never been detected by 
actual observation. It is simply assumed in order to account 
for certain facts, and it is asserted that such a circulation must 
take place as a physical necessity. I freely admit that were it 
not that the warm water of equatorial regions is being con- 
stantly carried off by means of ocean currents such as the Ghilf- 
stream, it would accumulate till, in order to restoration of 
equilibrium, such a general movement as is supposed would be 
generated. But it will be shown that the warm water in equa- 
torial regions is being drained off so rapidly by ocean currents 
that the actual density of an equatorial column differs so little 
from that of a polar column that the force of gravity resulting 
from that difference is so infinitesimal that it is doubtful 
whether it is sufficient to produce sensible motion. I have also 
shown in Chapter YIU. that all the facts which this theory is 
designed to explain are not only explained by the wind theory, 
but are deducible from it as necessary consequences. In Qhapter 
XI. it is proved, by contrasting the quantity of heat conveyed 
by ooean currents from inter- tropical to temperate and polar 
regions with such an amount as could possibly be conveyed by 
means of a general oceanic circulation, that the latter sinks 
into insignificance before the former. In Chapters X. and XII. 
the various objections which have been advanced by Dr. 
Carpenter and Mr. Findlay are discussed at considerable length, 
and in Chapter IX. I have entered somewhat minutely into an 
examination of the mechanics of the gravitation theory. A 
statement of the wind theory is given in Chapter XIII. ; and 
in Chapter XIY. is shown the relation of this theory to the 



INTRODUCTION. 19 

theory of Secular changes of climate. This terminates the part 
of the inquiry relating to oceanic circulation. 

We now come to the crucial test of the theories respecting 
the cause of the glacial epoch, viz., Warm Inter-glacial Periods. 
In Chapters XY. and XYL I have given a statement of the 
geological facts which go to prove that that long epoch known 
as the Glacial was not one of continuous cold, but consisted of a 
succession of cold and warm periods. This condition of things 
is utterly inexplicable on every theory of the cause of the 
glacial epoch which has hitherto been advanced ; but, accord- 
ing to the physical theory of secular changes of climate under 
consideration, it follows as a necessary consequence. In fact, the 
amount of geological evidence which has already been accumu- 
lated in reference to inter-glacial periods may now be regarded 
as perfectly sufficient to establish the truth of that theory. 

If the glacial epoch resulted from some accidental distribu- 
tion of sea and land, then there may or may not have been 
more than one glacial epoch, but if it residted from the cause 
which we have assigned, then there must have been during the 
geological history of the globe a succession of glacial epochs 
corresponding to the secular variations in the eccentricity of 
the earth's orbit. A belief in the existence of recurring glacial 
epochs has been steadily gaining ground for many years past. 
I have, in Chapter XYIII., given at some length the facts on 
which this belief rests. It is true that the geological evidence 
of glacial qxxshs in prior ages is meagre in comparison with 
that of the glacial epoch of Post-tertiary times ; but there is a 
reason for this in the nature of geological evidence itself. 
Chapter XYII. deals with the geological records of former 
glacial epochs, showing that they are not only imperfect, but 
that there is good reason why they should be so, and that the 
imperfection of the records in reference to them cannot be 
advanced as an argument against their existence. 

If the glacial epoch resiilted from a high condition of eccen- 
tricity, we have not only a means of determining the positive 
date of that epoch, but we have also a means of determining 



to CLIMATE AND TIME. 

geological time in absolute measure. For if the glacial epooba 
of prior ages correspond to periods of high eccentricity, then 
the intervals between those periods of high eccentricity become 
the measure of the intervals between the glacial epochs. The 
researches of Lagrange and Leverrier into the secular variations 
of the elements of the orbits of the planets enable us to deter- 
mine with tolerable accuracy the values of the eccentricity of 
the earth's orbit for, at least, four millions of years past and 
future. With the view of determining those values, I several 
years ago computed from Leverrier's formula the eccentricity 
of the earth's orbit and longitude of the perihelion, at intervals 
of ten thousand and fifty thousand years during a period of 
three millions of j^ears in the past, and one million of years in 
the future. The tables containing these values will be found 
in Chapter XIX. These tables not only give us the date of the 
glacial epoch, but they afford, as will be seen from Chapter 
XXI., evidence as to the probable date of the Eocene and 
Miocene periods. 

Ten years ago, when the theory was first advanced, it was 
beset by a very formidable difficulty, arising from the opinions 
which then prevailed in reference to geological time. One or 
two glacial epochs in the course of a million of years was a 
conclusion which at that time scarcely any geologist would 
admit, and most would have felt inclined to have placed the 
last glacial epoch at least one million of years back. But then 
if we assume that the glacial epoch was due to a high state of 
eccentricity, we should be compelled to admit of at least two 
glacial epochs during that lapse of time. It was the modern 
doctrine that the great changes undergone by the earth's crust 
were produced, not by convulsions of nature, but by the slow 
and almost imperceptible action of rain, rivers, snow, frost, ice, 
&c., which impressed so strongly on the mind of the geologist 
the vast duration of geological periods. When it was con* 
sidered that the rocky face of our globe had been carved into 
hills and dales, and ultimately worn down to the sea-level by 
means of those apparently trifling agents, not only once or 
twice, but many times, during past ages, it was not surprising 



INTRODUCTION. si 

tliat the views entertained by geologists regarding the immense 
antiquity of oar globe should not have harmonised with the 
deductions of physical science on the subject. It had been 
shown by Sir William Thomson and others, from physical 
considerations relating to the age of the sun's heat and the 
secular cooling of our globe, that the geological history of our 
earth's crust must be limited to a period of something like one 
hundred millions of years. But these speculations had but little 
weight when pitted against the stem and undeniable facts of 
sub-aerial denudation. How, then, were the two to be recon- 
ciled ? Was it the physicist who had under-estimated geolo- 
gical time, or the geologist who had over-estimated it P Few 
familiar with modem physics, and who have given special 
attention to the subject, would admit that the sun could have 
been dissipating his heat at the present enormous rate for a 
period much beyond one hundred millions of years. The proba- 
bility was that the amount of work performed on the earth's 
crust by the denuding agents in a period so inunense as a 
million of years was, for reasons stated in Chapter XX., very 
much under-estimated. But the di£ELCulty was how to prove 
this. How was it possible to measure the rate of operation of 
agents so numerous and diversified acting with such extreme 
slowness and irregularity over so immense areas P In other 
words, how was it possible to measure the rate of sub-aerial 
denudation P Pondering over this problem about ten years 
ago, an extremely simple and obvious method of solving it sug- 
gested itself to my mind. This method — the details of which 
will be found in Chapter XX. — showed that the rate of sub- 
aerial denudation is enormously greater than had been supposed. 
The method is now pretty generally accepted, and the result has 
already been to bring about a complete reconciliation between 
physics and geology in reference to time. 

Chapter XXI. contains an account of the gravitation theories 
of the origin of the sun's heat. The energy possessed by the 
sun is generally supposed to have been derived from gravita- 
tion, combustion being totally inadequate as a source. But 
something more th/in cavitation is required before "W^ ^AiTi 



II CLIMATE AND TIME. 

account for OTen one hundred millions of years' heat. Oravitation 
could not supply even one-half that amount. There must be 
tome other and greater source than that of gravitation. There 
isy however, as is indicated, an obvious source from which &r 
more energy may have been derived than could have been 
obtained from gravitation. 

The method of determining the rate of sub-aerial denudatioiii 
enables us also to arrive at a rough estimate of the actual mean 
thickness of the stratified rocks of the globe. It will be seen 
from Chapter XXII. that the mean thickness is far less than 
i« generally supposed. 

The physical cause of the submergence of the land during 
the glacial epoch, and the influence of change in the obliquity 
of the ecliptic on climate, are next considered. In Chapter 
XXVI. I have given the reasons which induce me to believe 
that coal is an inter-glacial formation. 

The next two chapters — the one on the path of the ice in 
north-western Europe, the other on the north of England 
ice-sheet — are reprints of papers which appeared a few years 
ago in the Oeological Magazine, Recent observations have con- 
firmed the truth of the views advanced in these two chapters, 
and they are rapidly gaining acceptance among geologists. 

I have given, at the conclusion, a statement of the molecular 
theory of glacier motion — a theory which I have been led to 
modify considerably on one particular point. 

There is one point to which I wish particularly to direct 
attention — viz., that I have studiously avoided introducing into 
the theories propounded anything of a hypothetical nature* 
There is not, so fur as I am aware, &om beginning to end of 
this volume, a single hypothetical element : nowhere have I 
attempted to give a hypothetical explanation. The conclusions 
are in every case derived either from facts or from what I 
believe to be admitted principles. In short, I have aimed to 
prove that the thiH>ry of secular changes of climate follows^ as 
a necessary consequence, from the admitted principles of 
physical science. 



CHAPTER II. 

OCXAH-CURRSXTS Il« RELATION TO THK mSTBIBTTTIOV 
OF HEAT OVER THE GLOBS. 

rike abeolate Healing-power of Ocean-currents. — ^Volome of the Gnlf-stream.— 
Abeoluto Amount of Heat conveyed b^ it. — Greater Portion of Moiatnre in 
inter-tropical Regions faOa as Rain in those Regiont. — Land along the 
Equator tends to lower the Temperature of the Globe. — ^Influence of 
Golf-stream on Climate of Europe. — ^Temperature of Space. — Radiation of 
a Particle. — Profeosor Dove on Normal Temperataro. — Temperature of 
Equator and Poles in the Absence of Ocaan-currents.— Temperature of 
Londoo, how much due to Ocean-currents. 

I'he absolute Heating-power of Ocean-eurrenia. — ^There is 
perhaps no physical agent concerned in the distribution of heat 
oyer the sarface of the globe the influence of which has been so 
much underrated as that of ocean-currents. This is, no doubt, 
owing to the fact that although their surface-temperature, 
direction, and general influence have obtained considerable 
attention, yet little or nothing has been done towards deter- 
mining the absolute amount of heat or of cold conveyed by 
them or the resulting absolute increase or decrease of tern- 
perature. 

The modem method of determining the amount of heat- 
effects in absolute measure is, doubtless, destined to cast new 
light on all questions connected with climate, as it has done, and 
is still doing, in every department of physics where energy, 
under the form of heat, is being studied. But this method has 
hardly as yet been attempted in questions of meteorolo^jry ; and 
owing to the complicated nature of the phenomena i;vith which 
the meteorologist has generally to deal, its application will 
very often prove practically impossible. Nevertheless, it is 
particularly suitable to all questions relating to the direct 



14 CLIMATE AND TIME. 

thermal eflFects of currents, whatever the nature of these currents 
may happen to be. 

In the application of the method to an ocean-ciirrent, the 
two most important elements required as data are the volume 
of the stream and its mean temperature. But although we 
know something of the temperature of most of the great ocean- 
currents, yet, with the exception of the Gull-stream, little has 
been ascertained regarding their volume. 

The breadth, depth, and temperature of the Gulf-stream 
have formed the subject of extensive and accurate observations 
by the United States Coast Survey. In the memoirs and charts 
of that survey cross-sections of the stream at various places are 
given, showing its breadth and depth, and also the temperature 
of the water from the surface to the bottom. "We are thus 
enabled to determine with some precision the mean tempera- 
ture of the stream. And knowing its mean velocity at any 
g^ven section, we have likewise a means of determining the 
number of cubic feet of water passing through that section in a 
given time. But although we can obtain with tolerable accu- 
racy the mean temperature, yet observations regarding the. 
velocity of the water at all depths have unfortunately not been 
made at any particular section. Consequently we have no 
means of estimating as accurately as we could wish the volume 
of the current. Nevertheless, since we know the surface- velo- 
city of the water at places where some of the sections were 
taken, we are enabled to make at least a rough estimate of the 
volume. 

From an examination of the published sections, I came to the 
conclusion some years ago* that the total quantity of water 
conveyed by the stream is probably equal to that of a stream 
fifty miles broad and 1,000 feet deep,t flowing at the rate of 

• Phil. Mag. for February, 1867, p. 127. 

t The Gult-stream at the narrowedt place examined by the Coast Sarvey, and 
where also its velocity was greatest, was found to be over du stntute miles bioad 
and 1,950 feet deep. But we must not suppose that this represents all the warm 
water which is received by the Atlantic from the equator ; a great mass flows 
into the Atlantic without passing through the Straits of Florida. 



DISTRIBUTION OF HEAT 15 

fonr miles an hour, and that the mean temperature of the entire 
maas of moying water is not tmder 65" at the moment of 
leaving the Gkdf. But to prevent the possibility of any objeo- 
tionB being raised on the grounds that I may have over-esti- 
mated the yolume of the stream, I shall take the velocity to be 
two miles instead of four miles an hour. We are warranted, I 
think, in concluding that the stream before it returns from its 
northern journey is on an average cooled down to at least 40^,* 
consequently it loses 25^ of heat. Each cubic foot of water, 
therefore, in this case carries from the tropics for distribution 
upwards of 1,158,000 foot-pounds of heat. According to the 
above estimate of the size and velocity of the stream, which 
in Chapter XL will be shown to be an under-estimate, 
2,787,840,000,000 cubic feet of water are conveyed fix)m the 
Gulf per hour, or 66,908,160,000,000 cubic feet daily. Conse- 
quently the total quantity of heat thus transferred per day 
amounts to 77,479,660,000,000,000,000 foot-pounds. 

This estimate of the volume of the stream is considerably less 
by one-half than that given both by Captain Maury and by Sir 
John Herschel. Captain Maury considers the Gulf-stream equal 
to a streai]|^ thirty-two miles broad and 1,200 feet deep, flowing 
at the rate of five knots an hour.t This gives 6,166,700,000,000 
cubic feet per hour as the quantity of water conveyed by this 
stream. Sir John Herschers estimate is still greater. He con- 
siders it equal to a stream thirty miles broad and 2,200 feet 
deep, flowing at the rate of four miles an hour. % This makes 
the quantity 7,369,900,000,000 cubic feet per hour. Dr. Cold- 
ing, in his elaborate memoir on the Gnlf-stream, estimates the 
volume at 6,760,000,000,000 cubic feet per hour, while Mr. 
Laughton's estimate is nearly double that of mine. 

• It is probable that a large proportion of the water conatituting the aouth 
flttstem branch of the Q-ulf-stream ia never cooled down to 4C^ ; but, on the other 
hand* the north-eaatezn branch, whidi paases into the arctic regioni, will )fe 
cooled far below 40", probably below 30". Hence I cannot be over-eetimating 
the extent to which the water of the aulf-stream ii cooled down in fixing upon 
40* as the average minimum temperature. 

t ** Phyiical Geography of the Sea," { 24, 6th edition. 

: ** Physical Geography ,*' { 64. 



2C CLIMATE AND TIME. 

Fnjtn obsenrations made by Sir John Hencbel and hj IL 
Pouiilet on the direct heat of the san, it is found that^ weze no 
h«at absorbed by the atmosphere, about eighty-three foot-ponnda 
per ser^iiid would fall upon a square foot of surfisu^e placed at right 
angle* Uj the sun's rays.* Mr. Meech estimates that the qoanti^ 
of heat cut off by the atmosphere is equal to about twenty-two 
per cent, of the total amount received &om the sun. M. Pooillot 
tmiiuuiUtB the loss at twenty-four per cent. Taking the former 
evtimate, 64'74 foot-pounds per second will therefore be the 
quantity of heat falling on a square foot of the earth's anrfaoe 
when the sun is in the zenith. And were the sun to remain 
stationary in the zenith for twelve hours, 2,796,768 foot-pounds 
would fall upon the surface. 

it can be shown that the total amount of heat received upon 
a unit surface on the equator, during the twelve hours from 
sunrise till sunset at the time of the equinoxes, is to the total 
amount which would be received upon that surface, were the 
sun to remain in the zenith during those twelve hours, as the 
diameter of a circle to half its circumference, or as 1 to 1*5708. 
It follows, therefore, that a square foot of surface on the equator 
receives from the sun at the time of the equinoxes 1,780,474 
foot-pounds daily, and a square mile 49,636,760,000,000 foot* 
{Kiunds daily. But this amounts to only l-1560935th part of 
the quantity of heat daily conveyed from the tropics by the 
Gulf •stream. In other words, the Gulf-stream conveys as 
much heat as is received from the sun by 1,560,935 square 
miles at the equator. The amount thus conveyed is equal to 
all the heat which falls upon the globe within thirty-two miles 
on each side of the equator. According to calculations made by 
Mr. Moccb,t the annual quantity of heat received by a unit 
surface on the frigid zone, taking the mean of the whole zone, 
is 5'45-12th of that received at the equator; consequently the 
quantity of heat conveyed by the Gulf-stream in one year is 

* Timni. of Roy. Soc. of EJin., vol. xxi., p. 67. PhiL Hag., { i, yoL is. 
p. £6. 
t ** Smithiouian Coniributioni to Knowledge/* vol. ix. 



DISTRIBUTION OF HE A T. tj 

equal to the heat whioh fcdls on an average on 3,436,900 square 
milea of the arctic regions. The frigid zone or arctic regions 
Mmtain SyldO^OOO square miles. There is actually, therefore, 
nearly one-half as much heat transferred from tropical regions 
by the Gulf-stream as is recexved from the sun by the entire 
arctic regicms, the quantity conveyed from the tropics by the 
stream to that received from the sun by the arctic regions being 
nearly as two to five. 

But we have been assuming in our calculations that the per- 
centage of heat absorbed by the atmosphere is no greater in 
polar regions than it is at the equator, which is not the case. If 
we make due allowance for the extra amount absorbed in polar 
r^ona in consequence of the obliqueness of the sun's rays, the 
total quantity of heat conveyed by the Gulf-stream will pro- 
bably be nearly equal to one-half the amount received from the 
sun by the entire arctic regions. 

If we compare the quantity of heat conveyed by the Gulf- 
stream with that conveyed by means of aerial currents, the 
result is equally startling. The density of air to that of water 
is as 1 to 770, and its specific heat to that of water is as 1 to 
4*2 ; consequently the same amount of heat that would raise 
1 cubic foot of water 1° would raise 770 cubic feet of air 4°'2, 
or 3,234 cubic feet 1^. The quantity of heat conveyed by the 
Gulf-stream is therefore equal to that which would be convoyed 
by a current of air 3,234 times the volume of the Gulf-stream, 
at the same temperature and moving with the same velocity. 
Taking, as before, the width of the stream at fifty miles, and 
its depth at 1,000 feet, and its velocity at two miles an hour, 
it follows that, in order to convey an equal amount of heat 
from the tropics by means of dtn aerial current, it would be 
necessary to have a current about 1^ mile deep, and at the 
temperature of 65°, blowing at the rate of two miles an hour 
from every part of the equator over the northern hemisphere 
towards the pole. If its velocity were equal to that of a good 
sailing-breeze, which Sir John Herschol states to be about 
twenty -one miles an hour, the current would require to be 



28 CLIMATE AND TIME, 

above 600 feet deep. A greater quantity of heat is probably 
conveyed by the Gulf-stream alone from the tropical to the 
temperate and arctic regions than by all the aerial currents 
which flow from the equator. 

We are apt, on the other hand, to over-estimate the amount 
of the heat conveyed from tropical regions to us by means 
of aerial currents. The only currents which flow from the 
equatorial regions are the upper currents, or anti-trades as they 
are called. But it is not possible that much heat can be con- 
veyed directly by them. The upper currents of the trade- 
winds, even at the equator, are nowhere below the snow-line ; 
they must therefore lie in a region of which the temperature is 
actually below the freezing-point. In fact, if those currents 
were warm, they would elevate the snow-line above themselves. 
The heated air rising off the hot burning ground at the equator, 
after ascending a few miles, becomes exposed to the intense cold 
of the upper regions of the atmosphere ; it then very soon loses 
all its heat, and returns from the equator much colder than it 
went thither. It is impossible that we can receive any heat 
directly from the equatorial regions by means of aerial cur- 
rents. It is perfectly true that the south-west wind, to which 
we owe so much of our warmth in this country, is a con- 
tinuation of the anti-trade ; but the heat which this wind brings 
to us is not derived from the equatorial regions. This will 
appear evident, if we but reflect that, biefore the upper cur- 
rent descends to the snow-line after leaving the equator, it 
must traverse a space of at least 2,000 miles ; and to perform 
this long journey several days will be required. During all 
this time the air is in a region below the freezing-point ; and 
it is perfectly obvious that by the time it begins to descend it 
must have acquired the temperature of the region in which it 
has been travelling. 

If such be the case, it is evident that a wind whose tempera- 
ture is below 32° could never warm a country such as ours, 
where the temperature does not fall below 38° or 39°. The 
heat of our south-west winds is derived, not directlv from the 



DISTRIBUTION OF HEA T. 29 



equator, but from the warm water of the AtLmtic — in fact, 
from the Gulf-stream. The upper current acquires its heat 
after it descends to the earth. There is one way, however, 
whereby heat is indirectly conveyed from the equator by the 
anti-trades; that is, in the form of aqueous vapour. In the 
formation of one pound of water from aqueous vapour, as 
Professor Tyndall strikingly remarks, a quantity of heat is 
given out sufficient to melt five pounds of cast iron.* It must, 
however, be borne in mind that the greater part of the mois- 
ture of the south-west and west winds is derived from the 
ocean in temperate regions. The upper current receives the 
greater part of its moisture after it descends to the earth, whilst 
the moisture received at the equator is in great part condensed, 
and falls as rain in those regions. 

This latter assertion has been so frequently called in question 
that I shall give my reasons for making it. According to Dr. 
Keith Johnston (''Physical Atlas ") the mean rainfall of the torrid 
regions is ninety-six inches per annum, while that of the tem- 
perate regions amounts to only thirty-seven inches. If the 
greater part of the moisture of the torrid regions does not fall 
as rain in those regions, it must full as such beyond them. 
Now the area of the torrid to that of the two temperate regions 
is about as 39*3 to 51. Consequently ninety-six inches of 
rain spread over the temperate regions would give seventy-four 
inches ; but this is double the actual rainfall of the temperate 
regions. If, again, it were spread over both temperate and 
polar regions this would yield sixty-four inches, which, how- 
ever, is nearly double the mean rainfall of the temperate and 
polar regions. If we add to this the amount of moisture de* 
rived from the ocean within temperate and polar regions, wo 
should have a far greater rainfall for these latitudes than for 
the torrid region, and we know, of course, that it is actually 
far less. This proves the truth of the assertion that by far the 
greater part of the moisture of the torrid regions falls in those 
regions as rain. It will hardly do to object that the above may 

• '' Heat us tt M( de of Motion,'* art 240. 



Il^ 



JO CLIMATE AND TIME, 

proliably be an over-estimate of the amount of rain&ll in tlie 
iffrrid zone, for it is not at all likely that any error will ever 
b^ found which will affect the general conclusion at which we 
have arrived. 

Dr. Carpenter, in proof of the small rainfall of the torrid 
»me, adduces the case of the Bed Sea, where, although evaponip 
iion is excessive, almost no rain falls. But the reason why the 
vapour raised from the Bed Sea does not fall in that region as 
rain, is no doubt owing to the &ci that this sea is only a narrow 
strip of water in a dry and parched land, the air above which 
is too greedy of moisture to admit of the vapour being deposited 
as rain. Over a wide exptmse of ocean, however, where the air 
above is kept to a great extent in a constant state of saturation^ 
the case is totally different. 

Land at the Equator tendn to Lotcer the Temperature of the 
Olohe, — The foregoing considerations, as well as many others 
which might be stated, lead to the conclusion that, in order to 
raise the mean temperature of the whole earth, water should be 
placed along the equator, and not landj as is supposed by Sir 
Charles Lyell and others. For if land is placed at the equator, 
the possibility of conveying the sun's heat from the equatorial 
regions by means of ocean-currents is prevented. The trans- 
ference of heat could then be effected only by meanax>f the 
upper currents of the trades ; for the heat conveyed by conduction 
along the solid crust, if any, can have no sensible effect on 
climate. But these currents, as we have just seen, are ill- 
adapted for conveying heat. 

The surface of the ground at the equator becomes intensely 
heated by the sun's rays. This causes it to radiate its heat 
more rapidly into space than a surface of water hisated under 
the same conditions. Again, the air in contact with the hot 
ground becomes also more rapidly heated than in contact with 
water, and consequently the ascending current of air carries off 
a greater amount of heat. But were the heat thus carried away 
transferred by means of the upper currents to high latitudea 

d there employed to warm the earth, then it might to a con- 



DISTRIBUTION OF HEAT ji 

nderable extent compensate for the absence of ocean-currents, 
and in this case land at the equator might be nearly as well 
adapted as water for raising the temperature of the whole earth. 
But sach is not the case; for the heat carried up bj the 
ascending current at the equator is not employed in warming 
the earthy but is thrown off into the cold stellar space above. 
This ascending current, instead of being employed in warming 
the globe, is in reality one of the most effectual means that the 
earth has of getting quit of the heat received from the sun, and 
of thus maintaining a much lower temperature than it would 
otherwise possess. It is in the equatorial regions that the earth 
loses as well as gains the greater part of its heat ; so that, of 
all places, here ought to be placed the substance best adapted 
for preventing the dissipation of the earth's heat into space, in 
order to raise the general temperature of the earth. Water, 
of all substances in nature, seems to possess this quality to the 
greatest extent ; and, besides, it is a fluid, and therefore adapted 
by means of currents to carry the heat which it receives from 
the sun to every region of the globe. 

These results show (although they have reference to only 
one stream) that the general influence of ocean-currents on the 
distribution of heat over the surface of the globe must be very 
great. If the quantity of heat transferred from equatorial 
regions by the G^lf-stream alone is nearly equal to all the heat 
received from the sun by the arctic regions, then how enormous 
must be the quantity conveyed from equatorial regions by all 
the ocean-currents together ! 

Influence of the Oulf-Biream on the Climate of £urop*\ — In a 
paper read before the British Association at Exeter, Mr. A. 6. 
Findlay objects to the conclusions at which I have arrived in 
former papers on the subject, that I have not taken into account 
the great length of time that the water requires in order to 
circulate, and the interference it has to encounter in its passage. 

The objection is, that a stream so comparatively small as the 
Gulf-streum, after spreading out over such a large area of the 
Atlantic, and moving so slowly across to the shores of Europe. 
8 



32 CLIMATE AND TIME. 

losing heat all the way, would not be able to produce any very 
sensible influence on the climate of Europe. 

I am unable to perceive the force of this objection. Why, 
the very efficiency of the stream as a heating agent necessarily 
depends upon the slowness of its motion. Did the Gulf-stream 
move as rapidly along its whole course as it does in the Straits 
of Florida, it could produce no sensible effect on the climate of 
Europe. It does not require much consideration to perceive 
this. (1) If the stream during its course continued narrow, 
deep, and rapid, it would have little opportunity of losing its 
heat, and the water would carry back to the tropics the heat 
which it ought to have given off in the temperate and polar 
regions. (2) The Gulf-stream does not heat the shores of 
Europe by direct radiation. Our island, for example, is not 
heated by radiation from a stream of warm water flowing along 
its shores. The Gulf-stream heats our island indirectly by 
heating the winds which blow over it to our shores. 

The anti-trades, or upper return-currents, as we have seen, 
bring no heat from the tropical regions. After traversing some 
2,000 miles in a region of extreme cold they descend on the 
Atlantic as a cold current, and there absorb the heat and 
moisture which they carry to north-eastern Europe, Those 
aerial currents derive their heat from the Gulf-stream, or if it 
is preferred, from the warm water poured into the Atlantic by 
the Gulf- stream. 

How, then, are these winds heated by the warm water P 
The air is heated in two wavv*?, viz., by direct radiation from the 
water, and by contact with the water. Now, if the Gulf-stream 
continued a narrow and d3ep current during its entire course 
similar to what it is at the Straits of Florida, it could have 
little or no opportunity of communicating its heat to the air 
either by radiation or by contact. If the stream were only 
about forty or fifty miles in breadth, the aerial particles in 
their passage across it would not be in contact with the warm 
water more than an hour or two. Moreover, the number of par- 
ticles in contact with tb^ water, owing to the narrowness of the 



DISTRIBUTION OF HE A T. 33 

stream, would be small, and there would therefore be little 
opportunity for the air becoming heated by contact. The same 
also holds true in regard to radiation. The more we widen 
the stream and increase its area, the more we increase its 
radiating surface; and the greater the radiating surface, the 
greater is the quantity of heat thrown off. But this is not all ; 
the number of aerial particles heated by radiation increases in 
proportion to the area of the radiating surface ; consequently, 
the wider the area over which the waters of the Gulf- stream 
are spread, the more effectual will the stream be as a heating 
agent. And, again, in order that a very wide area of the 
Atlantic may be covered with the warm waters of the stream, 
slowness of motion is essential. 

Mr. Findlay supposes that fully one-half of the Gulf-stream 
pas83s into the south-eastern branch, and that it is only the 
north-eastern branch of the current that can be effectual in 
raising the temperature of Europe. But it appears to me that 
it is to this south-eastern portion of the current, and not to the 
north-eastern, that we, in this country, are chiefly indebted for 
our heat. The south-west winds, to which we owe our heat, 
derive their temperature from this south-eastern portion which 
flows away in the direction of the Azores. The south-west 
winds which blow over the northern portion of the current 
which flows past our island up into the arctic seas cannot 
possibly cross this country, but will go to heat Norway and 
northern Europe. The north-eastern portion of the stream, no 
doubt, protects us from the ice of Greenland by warming the 
north-west winds which come to us from that cold region. 

Mr. Buchan, Secretary of the Scottish Meteorological Society, 
has shown* that in a large tract of the Atlantic between lati- 
tudes 20^ and 40° N., the mean pressure of the atmosphere is 
greater than in any other place on the globe. To the west of 
Madeira, between longitude 10° and 40° W., the mean annual 
pressure amounts to 30*2 inches, while between Iceland and 
Spitzbergen it is only 29*6, a lower mean pressure than is found 

♦ Tr iiis. Roy. Soc. of Edin., vol. xxv., part 2. 



j4 CLIMATE AND TIME. 

in any other place on the northern hemisphere. There must 
consequently, he concludes, be a general tendency in the air to 
flow from the former to the latter place along the earth's sur- 
face. Now, the air in moving from the lower to the higher 
latitudes tends to take a north-easterly direction, and in this 
case will pass over our island in its course. This region of 
high pressure, however, is situated in the very path of the 
south-eastern branch of the Gulf -stream, and consequently the 
winds blowing therefrom will carry directly to Britain the heat 
of the Oulf-stream. 

As we shall presently sec, it is as essential to the heating of 
our island as to that of the southern portion of Europe, that a 
very large proportion of the waters of the Gulf-stream should 
spread over the surface of the Atlantic and never pass up into 
the arctic regions. 

Even according to Mr. Findlay*s own theory, it is to the 
south-west wind, heated by the warm waters of the Atlantic, 
that we are indebted for the high temperature of our climate. 
But he seems to be under the impression that the Atlantic 
would be able to supply the necessary heat independently of 
the Gulf-stream. This, it seems to me, is the fimdamental 
error of all those who doubt the efficiency of the stream. It is 
a mistake, however, into which one is very apt to fall who does 
not adopt the more rigid method of determining heat-results in 
absolute measure. When we apply this method, we find that 
the Atlantic, without the aid of such a current as the Gulf- 
stream, would be wholly unable to supply the necessary amount 
of heat to the south-west winds. 

The quantity of heat conveyed by the Gulf -stream, as we 
have seen, is equal to all the heat received from the sun by 
1,560,935 square miles at the equator. The mean annual quan- 
tity of heat received from the sun by the temperate regions per 
unit surface is to that received by the equator as 908 to 12.* 
Consequently, the quantity of heat conveyed by the stream is 
equal to all the heat received from the sun by 2,062,960 square 

♦ See ** Smithsonian Coiitributiona to Knowledge,'* vol. ix. 



DISTRIBUTION OF HEAT. 35 

miles of the ten^>erate regions. The total area of the Atlantic 
from the latitude of the Straits of Florida, 200 miles north 
of the tropic of Cancer, up to the Arctic Circle, including al80 
the Oerman Ocean, is ahout 8,500,000 square miles. lu this 
case the quantity of heat carried by the Gulf-stream into the 
Atlantic through the Straits of Florida, is to that received by 
this entire area from the sun as 1 to 4*12, or in round numbers 
as 1 to 4. It therefore follows that one-fifth of all the heat 
possessed by the waters of the Atlantic over that area, even 
supposing that they absorb every ray that falls upon them, is 
derived from the Gulf- stream. Would those who call in ques-' 
tion the efficiency of the Gulf-stream be willing to admit that 
a decrease of one-fourth in the total amount of heat received 
from the sun, over the entire area of the Atlantic from within 
200 miles of the tropical zone up to the arctic regions, would 
not sensibly affect the climate of northern Europe P If they 
would not willingly admit this, why, then, contend that the Gulf- 
stream does not affect climate P for the stoppage of the Gulf- 
stream would deprive the Atkntic of 77,479,650,000,000,000,000 
foot-pounds of energy in the form of heat per day, a quantity 
equal to one-fourth of all the heat received from the sun by 
that area. 

How much, then, of the temperature of the south-west winds 
derived from the water of the Atlantic is due to the Gulf- 
stream P 

Were the sun extinguished, the temperature over the whole 
earth would sink to nearly that of stellar space, which, according 
to the investigations of Sir John Herschel * and of M. Pouillet, t 
is not above — 239° F. Were the earth possessed of no atmo- 
sphere, the temperature of its surface would sink to exactly that 
of space, or to that indicated by a thermometer exposed to no 
other heat-influence than that of radiation from the stars. But 
the presence of the atmospheric envelope would slightly modify 

•."Meteorology," tcfction 36. 

t Comptei'Emdut, July 9, 1838. Taylor's " ScicDtific Memoire/' vol. iv., p. 44 
(1S46). 



36 CLIMATE AND TIME. 

the condidons of things ; for the heat from the stars (which of 
course constitutes what is called the temperature of space) 
would, like the sun's heat, pass more freely through the atmo- 
sphere than the heat radiated back from the earth, and there 
would in consequence of this be an accumulation of heat on the 
earth's surface. The temperature would therefore stand a little 
higher than that of space ; or, in other words, it would stand a 
little higher than it would otherwise do were the earth exposed 
in space to the direct radiation of the stars without the atmo- 
spheric envelope. But, for reasons which will presently be 
stated, we may in the meantime, till further light is cast upon 
this matter, take — 239° F. as probably not far from what 
would be the temperature of the earth's surface were the sun 
extinguished. 

Suppose now that we take the mean annual temperature of 
the Atlantic at, say, 56°.» Then 239°+56°=z 295° represents 
the number of degrees of rise due to the heat which it receives. 
In other words, it takes all the heat that the Atlantic receives 
to maintain its temperature 295° above the temperature of space. 
Stop the Gulf-stream, and the Atlantic would be deprived of 
one-fifth of the heat which it possesses. Then, if it takes five 
parts of heat to maintain a temperature of 295° above that of 
space, the four parts which would remain after the stream was 
stopped would only be able to maintain a temperature of four- 
fifths of 295°, or 236° above that of space : the stoppage of the 
Gulf-stream would therefore deprive the Atlantic of an amount 
of heat which would be sufficient to maintain its temperature 
69° above what it would otherwise be, did it depend alone upon 
the heat received directly from the sun. It does not, of course, 
follow that the Gulf-stream actually maintains the temperature 
69° above what it would otherwise be were there no ocean- 
currents, because the actual heating-efiect of the stream is 
neutralized to a very considerable extent by cold currents from 

• The mean temperature of the Atlantic between the tropics and the arotio 
circle, aocording to Admiral Fitzroy's chart,- is about 60^ But he assigna far 
too high a temperature for latitudoa above 50^ It » probable that 66° ia not far 
from the truth. 



DISTRIBUTION OF HEAT 17 

the arotio r^ons. Bat 59^ of rise represents its actual power ; 
consequently Si^y minus the lowering effect of the cold currents, 
represents the actual rise. What the rise may amount to at 
any particular place must be determined by other means* 

This method of calculating how much the temperature of the 
earth's surface would rise or fall from an increase or a decrease 
in the absolute amount of heat received is that adopted by Sir 
John Herschel in his '' Outlines of Astronomy/' § 369*. 

About three years ago, in an article in the Reader^ I endea- 
voured to show that this method is not rigidly correct. It has 
been shown from the experiments of Dulong and Petit, Dr. 
Balfour Stewart, Professor Draper, and others, that the rate at 
which a body radiates its heat off into space is not directly pro- 
portionate to its absolute temperature. The rate at which a 
body loses its heat as its temperature rises increases more 
rapidly than the temperature. As a body rises in temperature 
the rate at which it radiates off its heat increases ; the rate of this 
increase, however, is not uniform, but increases with the tem- 
perature. Consequently the temperature is not lowered in 
proportion to the decrease of the sun's heat. But at the 
comparatively low temperature with which we have at present 
to deal, the error resulting from assuming the decrease of tem- 
perature to be proportionate to the decrease of heat would not 
be great. 

It may be remarked, however, that the experiments referred 
to were made on solids ; but, from certain results arrived at by 
Dr. Balfour Stewart, it would seem that the radiation of a 
material particle may be proportionate to its absolute tempera- 
ture.* This physicist found that the radiation of a thick plate 
of glass increases more rapidly than that of a thin plate as the 
temperature rises, and that, if we go on continually diminishing 
the thickness of the plate whose radiation at different tem- 
peratures we are asceitaining, we find that as it grows thinner 
and thinner the rate at which it radiates off its heat as its 
temperature rises becomes less and less. In other words, as the 

* The probable phyticel cause of this will be oonridered in the Appendix. 



j8 CLIMATE AND TIME. 

plate grows thinner and thinner its rate of radiation becomes 
more and more proportionate to its absolute temperature. And 
we can hardly resist the conviction that if we could possibly 
go on diminishing the thickness of the plate till we reached a 
film so thin as to embrace but only one particle in its thickness, 
its rate of radiation would be proportionate to its temperature. 
Dr. Balfour Stewart has very ingeniously suggested the probable 
reason why the rate of radiation of thick plates increases with 
rise of temperature more rapidly than that of thin. It is this : 
all substances are more diathermanous for heat of high tem- 
peratures than for heat of low temperatures. When a body 
is at a low temperature, we may suppose that only the exterior 
rows of particles supply the radiation, the heat fix)m the interior 
particles being all stopped by the exterior ones, the substance 
being very opaque for heat of low temperature ; while at a high 
temperature we may imagine that part of the heat from the 
interior particles is allowed to pass, thereby swelling the total 
radiation. But as the plate becomes thinner and thinner, the 
obstructions to interior radiation become less and less, and as 
these obstructions are greater for radiation at low temperatures 
than for radiation at high temperatures, it necessarily follows 
that, by reducing the thickness of the plate, we assist radiation 
at low temperatures more than we do at high. 

In a gas, where each particle may be assumed to radiate by 
it^f, and where the particles stand at a considerable distance 
from one another, the obstruction to interior radiation must be 
far less than in a solid. In this case the rate at which a gas 
radiates off its heat as its temperature rises must increase more 
slowly than that of a solid substance. In other words, its rate 
of radiation must correspond more nearly to its absolute tem- 
perature than that of a solid. If this be the cose, a reduction in 
the amount of heat received from the sun, owing to an increase 
of his distance, should tend to produce a greater lowering effect 
on the temperature of the air than it does on the temperature 
of the solid ground. But as the temperature of our climate is 
determined by the temperature of the air, it mu^^t follow that 



DISTRIBUTION OF HE A T. 59 

the error of aasuming that the decrease of temperature would 
be proportionate to the decrease in the intensity of the sun's 
heat may not be great. 

It may be observed here, although it does not bear directly 
on this point, that although the air in a room, for example, or 
at the earth's surface is principally cooled by convection rather 
than by radiation, yet it is by radiation alone that the earth's 
atmosphere parts with its heat to stellar space ; and this is the 
chief matter with which we are at present concerned. Air, like 
all other gases, is a bad radiator ; and this tends to protect it 
from being cooled to such an extent as it would otherwise be, 
were it a good radiator like solids. True, it is also a bad 
absorber ; but as it is cooled by radiation into space, and heated, 
not altogether by absorption, but to a very large extent by con- 
vection, it on the whole gains its heat more easily than it loses 
it, and consequently must stand at a higher temperature than 
it would do were it heated by absorption alone. 

But, to return ; the error of regarding the decrease of tem- 
perature as proportionate to the decrease in the amount of heat 
received, is probably neutralized by one of an opposite nature, 
viz., that of taking space at too high a temperature ; for by so 
doing we make the result too smalL 

We know that absolute zero is at least 493^ below the melt- 
ing-point of ice. This is 222° below that of space. Conse- 
quently, if the heat derived from the stars is able to maintain a 
temperature of — 239°, or 222° of absolute temperature, then 
nearly as much heat is derived from the stars as from the sun. 
But if so, why do the stars give so much heat and so very little 
light ? If the radiation from the stars could maintain a thermo- 
meter 222° above absolute zero, then space must be far more 
transparent to heat-rays than to light-rays, or else the stars 
give out a great amount of heat, but very little light, neither 
of which suppositions is probably true. The probability is, I 
venture to presume, that the temperature of space is not very 
much above absolute zero. At the time when these investi- 
gations into the probable temperature of space were made, at 



40 CLIMATE AND TIME. 

least as regards the labours of Pooillet, the modem scieooe of 
heat had no existence, and little or nothing was then known 
with certainty regarding absolute zero. In this case the whole 
matter would require to be reconsidered. The result of such 
an investigation in all probability would be to assign a lower 
temperature to stellar space than — 239^. 

Taking all these various considerations into account, it is 
probable that if we adopt — 239^ as the temperature of space, 
we shall not be far from the truth in assuming that the abso- 
lute temperature of a place above that of space is proportionate 
to the amount of heat received from the sun. 

"We may, therefore, in this case conclude that 59° of rise is 
probably not very far from the truth, as representing the influ- 
ence of the Gulf-stream. The Gulf-stream, instead of producing 
little or no effect, produces an effect far greater than is gene- 
rally supposed. 

Our island has a mean annual temperature of about 12° above 
the normal duo to its latitude. This excess of temperature has 
been justly attributed to the influence of the Gfulf-stream. But 
it is singular how this excess should have been taken as the 
measure of the rise resulting from the influence of the stream. 
These figures only represent the number of deg^rees that the 
mean normal temperature of our island stands above what is 
called the normal temperature of the latitude. 

The mode in which Professor Dove constructed his Tables of 
normal temperature was as follows : — He took the temperature 
of thirty-six equidistant points on every ten degrees of latitude. 
The mean temperature of these thirty-six points he calls in each 
case the normal temperature of the parallel. The excess above 
the normal merely represents how much the stream raises our 
temperature above the mean of all places on the same latitude, 
but it affords us no information regarding the absolute rise pro- 
duced. In the Pacific, as well as in the Atlantic, there are 
immense masses of water flowing from the tropical to the tem- 
perate regions. Now, unless we know how much of the normal 
temperature of a latitude is due to ocean -currents, and how 



DISTRIBUTION OF HEAT. 41 

much to the direct heat of the son, we could not posaibly, from 
Professor Dove's Tables, form the most distant conjecture as to 
how much of our temperature is derived from the Gulf-stream. 
The overlooking of this fact has led to a general misconception 
regarding the positive influence of the Gulf -stream on tempe- 
rature. The 12^ marked in Tables of normal temperature do 
not represent the absolute effect of the stream, but merely 
show how much the stream raises the temperature of our country 
above the mean of all places on the same latitude. Other places 
have their temperature raised by ocean-currents as well as this 
country; only the Gulf-stream produces a rise of several 
degrees over and above that produced by other streams in the 
same latitude. 

At present there is a difference merely of 80^ between the 
mean temperature of the equator and the poles ;* but were each 
part of the globe's surface to depend only upon the direct heat 
which it receives from the sim, there ought, according to theory, 
to be a difference of more than 200^. The annual quantity of 
heat received at the equator is to that received at the poles 
(supposing the proportionate quantity absorbed by the atmo- 
sphere to be the same in both cases) as 12 to 4*98, or, say, as 
12 to 5. Consequently, if the temperatures of the equator and 
the poles be taken as proportionate to the absolute amoimt of 
heat received from the sun, then the temperature of the equator 
above that of space must be to that of the poles above that of 
space as 12 to 5. What ought, therefore, to be the tempera- 
tures of the equator and the poles, did each place depend solely 
upon the heat which it receives directly from the sun P Were 
all ocean and aerial currents stopped, so that there could be no 
transference of heat from one part of the earth's surface to 
another, what ought to be the temperatures of the equator and 
the poles P We can at least arrive at a rough estimate on this 

• The mean temperature of the equator, according to Dove, is 79*** 7, and that 
of the north pole 2**8. But an there is, of course, some uncertainty regarding tlie 
actual mean temperature of the poles, we may take the difference in round 
numbers at 80". 



4.1 CLIMATE AND TIME. 

point. If we diminish the quantity of warm water conveyed 
from the equatorial regions to the temperate and arctic regions, 
the temperature of the equator will begin to rise, and that of 
the poles to sink. It is probable, however, that this process 
would affect the temperature of the poles more than it would 
that of the equator; for as the warm water flows from the 
equator to the poles, the area over which it is spread becomes 
less and less. But as the water from the tropics has to raise 
the temperature of the temperate regions as well as the polar^ 
the difference of effect at the equator and poles might not, on 
that account, be so very great. Let us take a rough estimate. 
Stiy that, as the temperature of the equator rises one degree, 
the temperature of the poles sinks one degree and a half. The 
mean annual temperature of the globe is about 58°. The mean 
temperature of the equator is 80°, and that of the poles 0°. Let 
ocean and aerial currents now begin to cease, the temperature 
of the equator commences to rise and the temperature of the 
poles to sink. For every degree that the temperature of the 
equator rises, that of the poles sinks 1^° ; and when the currents 
are all stopped and each place becomes dependent solely upon 
the direct rays of the sun, the niean annual temperature of the 
equator above that of space wiU be to that of the poles, above 
that of space, as 12 to 5. When this proportion is reached, the 
equator will be »374° above that of space, and the poles 156° ; 
for 374 is to 156 as 12 is to 5. The temperature of space we 
have seen to be — 239°, consequently the temperature of the 
equator will in this case be 135°, reckoned from the zero of the 
Fahrenheit thermometer, and the poles 83° below zero. The 
equator would therefore be 55° warmer than at present, and 
the poles 83° colder. The difference between the temperature 
of the equator and the poles will in this case amount to 218°. 

Now, if we take into account the quantity of positive energy 
in the form of heat carried by warm currents from the equator 
to the temperate and polar regions, and also the quantity of 
negative energy (cold) carried by cold currents from the polar 
regions to the equator, we shall find that they are sufficient to 



DISTRIBUTION OF HE A T 43 

reduce the difference of temperature between the polos and the 
equator from 218^ to 80^. 

The quantity of heat received in the latitude of London, for 
example, is to that received at the equator nearly as 12 to 8. 
This, according to theory, should produce a difference of 
about 125^. The temperature of the equator above that of 
space, as we have seen, would be 374°. Therefore 249° above 
that of space would represent the temperature of the latitude 
of London. This would give 10° as its temperature. The 
stoppage of all ocean and aerial currents would thus in- 
crease the difference between the equator and the latitude of 
London by about 85°. The stoppage of ocean-currents would 
not be nearly so much felt, of course, in the latitude of London 
as at the equator and the poles, because, as has been already 
noticed, in all latitudes midway between the equator and the 
poles the two sets of currents to a considerable extent com- 
pensate each other — ^the warm currents from the equator raise 
the temperature, while the cold ones from the poles lower it ; 
but as the warm currents chiefly keep on the surface and the 
eold return- currents are principally under-currents, the heating 
effect very greatly exceeds the cooling effect. Now, as we have 
seen, the stoppage of all currents would raise the temperature 
of the equator 55° ; tBat is to say, the rise at the equator alone 
would increase the difference of temperature between the 
equator and that of London by 55°. But the actual difference, 
as we have seen, ought to be 85° ; consequently the temperature 
of London would be lowered 30° by the stoppage of the cur- 
rents. For if we raise the temperature of the equator 55° and 
lower the temperature of London 30°, we then increase the 
difference by 85°. The normal temperature of the latitude of 
London being 40°, the stoppage of all ocean and aerial currents 
would thus reduce it to 10°. But the Gulf-stream raises the 
actual mean temperature of London 10° above the normal. Con- 
sequently 30° + 10°= 40° represents the actual rise at London 
due to the influence of the Gulf-stream over and above all the 
lowering effects resulting from arctic currents. On some parts 



H 



CLIMATE AND TIME. 



of the American shores on the latitude of London, the tern* 
perature is 10^ below the normal. The stoppage of all ocean 
and aerial currents would therefore lower the temperature there 
only 20°. 

It is at the equator and the poles that the great system of 
ocean and aerial currents produces its maximum effects. The 
influence becomes less and less as we recede from those places^ 
and between them there is a point where the influence of warm 
currents from the equator and of cold currents from the poles 
exactly neutralize each other. At this point the stoppage of 
ocean-currents would not sensibly affect temperature. This 
point, of course, is not situated on the same latitude in all 
meridians, but varies according to the position of the meridian 
in relation to land, and ocean-currents, whether cold or hot, 
and other circumstances. A line drawn round the globe through 
these various points would be very irregular. At one place, 
such as on the western side of the Atlantic, where the arctic 
current predominates, the neutral line would be deflected 
towards the equator, while on the eastern side, where warm 
currents predominate, the line would be deflected towards the 
north. It is a difficult problem to determine the mean position 
of this line ; it probably lies somewhere not far north of thfl 
tropics. 



CHAPTER in. 

3CKAN-UURRENTS IN RELATION TO THS DISTBIBimON OF HSAT 

OVER THE GLOBE. — (Continued.) 

Inflaencd of the Gulf-stream on the Climate of the Arctic RegionB. — Abeolate 
Amount of Heat received by the Arctic Regions from the Sun. — Influence of 
Ocean-currents shown by another Method. — Temperature of a Globe all 
Water or all Land according to Professor J. D. Forbes. — An important 
Consideration overlooked. — Without Ocean-currents the Globe would not be 
habitable. — Conclufiions not affected by Imperfection of Data. 

Influence of the Oulf-stream on the Climate of t/ie Arctic 
Regions. — Does the Gulf-stream pass into the arctic regions ? 
Are the seas around Spitzbergen and North Greenland heated 
bj the warm water of the stream P 

Those who deny this nevertheless admit the existence of an 
arctic current. They admit that an immense mass of cold water 
is continually flowing south from the polar regions around 
Greenland into the Atlantic. If it be admitted, then, that 
a mass of water flows across the arctic circle from north to 
south, it must also be admitted that an equal mass flows across 
from south to north. It is also evident that the water crossing 
from south to north must be warmer than the water crossing 
from north to south ; for the temperate regions are warmer 
than the arctic, and the ocean in temperate regions warmer 
than the ocean in the arctic ; consequently the current which 
flows into the arctic seas, to compensate for the cold arctic 
current, must be a warmer current. 

Is the Gulf- stream this warm current? Does this com- 
pensating warm current proceed from the Atlantic or from the 
Pacific? If it procoodfi from the Atlantic, it is simply the 



CLIMATE AND TIME. 

warm water of the Gulf- stream. We may call it the warm 
water of the Atlantic if we choose; but this camiot ma- 
terially affect the question at issue, for the heat which the 
waters of the Atlantic possess is derived, as we have seen, to 
an enormous extent from the water brought from the tropics 
by the Gulf-stream. If we deny that the warm compensating 
current comes from the Atlantic, then we must assume that it 
comes from the Pacific. But if the cold current flows from the 
arctic regions into the Atlantic, and the warm compensating 
current from the Pacific into the arctic regions, the highest 
temperature should be found on the Pacific side of the arctic 
regions and not on the Atlantic side ; the reverse, however, is 
the case. In the Atlantic, for example, the 41° isothermal 
line reaches to latitude 65° 30', while in the Pacific it nowhere 
goes beyond latitude 57°. The 27° isotherm reaches to lati- 
tude 75° in the Atlantic, but in the Pacific it does not pass 
beyond 64°. And the 14° isotherm reaches the north of Spitz- 
bergen in latitude 80°, whereas on the Pacific side of the arctic 
regions it does not reach to latitude 72°. 

On no point of the earth's surface does the mean annual 
temperature rise so high above the normal as in the northern 
Atlantic, just at the arctic circle, at a spot believed to be in the 
middle of the Gulf-stream. This place is no less than 22" "5 
above the normal, while in the northern Pacific the temperature 
does not anywhere rise more than 9° above the normal. These 
facts prove that the warm current passes up the Atlantic into 
the arctic regions and not up the Pacific, or at least that the 
larger amount of warm water must pass into the arctic regions 
through the Atlantic. In other words, the Gulf -stream is the 
warm compensating current. Not only must there be a warm 
stream, but one of very considerable magnitude, in order to 
compensate for the great amount of cold water that is constantly 
flowing from the arctic regions, and also to maintain the tem- 
perature of those regions so much above the temperature of 
space as they actually are. 

No doubt, when the results of the late dredging expedition 



DISTRIBUTION OF HEAT 47 

are published, they will cast much additional light on the 
direction and character of the currents forming the north* 
eastern branch of the Ghilf-stream. 

The average quantity of heat received by the arctic regions 
as a whole per unit surface to that received at the equator, as 
we have already seen, is as 5*45 to 12, assuming that the per* 
centage of rays cut off by the atmosphere is the same at both 
jdaces. In this case the mean annual temperature of the arctic 
regions, taken as a whole, would be about — 69^, did those 
regions depend entirely for their temperature upon the heat 
received directly from the sua. But the temperature would 
not even reach to this ; for the percentage of rays cut off by 
the atmosphere in arctic regions is generally believed to be 
greater than at the equator, and consequently the actual mean 
quantity of heat received by the arctic regions will be less than 
5-45-12ths of what is received at the equator. 

In the article on Climate in the " Encyclopaedia Britannica" 
there is a Table calculated upon the principle that the quantity 
of heat cut off is proportionate to the number of aerial particles 
which the rays have to encounter before reaching the surface of 
the earth — ^that, as a general rule, if the tracts of the rays follow 
an arithmetical progression, the diminished force with which 
the rays reach the ground will form a decreasing geometrical 
progression. According to this Table about 75 per cent, of the 
sun's rays are cut off by the atmosphere in arctic regions. If 
75 per cent, of the rays were cut off by the atmosphere in 
arctic regions, then the direct rays of the sun could not main- 
tain a mean temperature 100^ above that of space. But this 
is no doubt much too high a percentage for the quantity of heat 
cut off ; for recent discoveries in regard to the absorption of 
radiant heat by gases and vapours prove that Tables computed 
on this principle must be incorrect. The researches of Tyndall 
and Melloni show that when rays pass through any substance, 
the absorption is rapid at first : but the rays are soon ** sifted," 
as it is called, and they then pass onwards with but littls 
further obstruction. StiU, however, owing to the dense fogs 



^8 CLIMATE AND TIME. 

which prevail in arctic regions, the quantity of heat cut o£E 
must be considerable. If as much as 50 per cent, of the sun's 
rays are cut off by the atmosphere in arctic regions, the amount 
of heat received directly from the sun would not be sufficient to 
maintain a mean annual temperature of — 100^. Consequently 
the arctic regions must depend to an enormous extent upon 
ocean-currents for their temperature. 

Influence of Ocean-currenU shown by another Method. — That 
the temperature of the arctic regions would sink enormously, 
and the temperature of the equator rise enormously, were all 
ocean-currents stopped, can bo shown by another method — 
viz., by taking the mean annual temperature from the equator 
to the pole along a meridian passing through the ocean, say, 
the Atlantic, and comparing it with the mean annual tempera- 
ture taken along a meridian passing through a great continent, 
say, the Asiatic. 

Professor J. D. Forbes, in an interesting memoir,* has 
endeavoured by this method to determine what would be the 
temperature of the equator and the poles were the globe all water 
or all land. He has taken the temperature of the two meridians 
from the tables and charts of Professor Dove, and ascertained 
the exact proportion of land and water on every 1 0^ of latitude 
from the equator to the poles, with the view of determining 
what proportion of the average temperature of the globe in 
each parallel is due to the land, and what to the water which 
respectively belongs to it. He next endeavours to obtain a 
formula for expressing the mean temperature of a given parallel, 
and thence arrives at " an approximate answer to the inquiry 
as to what would have been the equatorial or polar temperature 
of the globe, or that of any latitude, had its surface been entirely 
composed of land or of water." 

The result at which he arrived is this : that, were the surface 
of the globe all water, 71^*7 would be the temperature of the 
equator, and 12°'5 the temperature of the poles ; and were the 

* Tram, of R07. Soc. Edin., vol. xxii., p. 76. 



DISTRIBUTION OF HEAT 49 

surface all land, 109^8 would be the temperature of the equator, 
and — 25^'6 the temperature of the poles. 

But in Professor Forbes's calculations no account whatever 
is taken of the influence of currents, whether of water or of 
air, and the difference of temperature is attributed wholly to 
difference of latitude and the physical properties of land and 
water in relation to their powers in absorbing and detaining 
the sun's rays, and to the laws of conduction and of conyection 
which regulate the internal motion of heat in the one and in 
the other. He considers that the effects of currents are all 
compensatory. 

" If a current of hot water," he says, " moderates the cold 
of a Lapland winter, the counter-current, which brings the cold 
of Greenland to the shores of the United States, in a great 
measure restores the balance of temperature, so far as it is dis- 
turbed by this particular influence. The prevalent winds, in 
like manner, including the trade-winds, though they render 
some portions of continents, on the average, hotter or colder 
than others, produce just the contrary effect elsewhere. Each 
continent, if it has a cold eastern shore, has likewise a warm 
western one; and even local winds have for the most part 
established laws of compensation. In a given parallel of lati- 
tude all these secondary causes of local climate may be imagined 
to be mutually compensatory, and the outstanding gradation of 
mean or normal temperature will mainly depend, 1st, upon the 
effect of latitude simply ; 2nd, on the distribution of land and 
water considered in their primary or statical effect/' 

It is singular that a physicist so acute as Professor Forbes 
should, in a question such as this, leave out of account the 
influence of currents, under the impression that their effects 
were compensatory. 

If there is a constant transference of hot water from the 
equatorial regions to the polar, and of cold water from tlie 
polar regions to the equatorial (a thing which Professor Forbes 
admitted), then there can only be one place between the equator 
and the pole where the two sets of currents compensate each 



50 CLIMATE AND TIME. 

other. At all places on the equatorial side of this point a 
cooling effect is the result. Starting from this neutral point, 
the preponderance of the cooling effect over the heating increases 
as we approach towards the equator, and the preponderance of 
the heating effect over the cooling increases as we recede from 
this point towards the pole — the cooling effect reaching a 
maximum at the equator, and the heating effect a masdmum at 
Uie pole. 

Had Professor Forbes obsened this important fact, he would 
have seen at once that the low temperature of the land in high 
latitudes, in comparison with that of the sea, was no index 
whatever as to how much the temperature of those regions 
would sink were the sea entirely removed and the surface to 
become land; for the present high temperature of the sea is 
not due wholly to the mere physical properties of water, but to 
a great extent is due to the heat brought by currents from the 
equator. Now, unless it is known how much of the absolute 
temperature of the ocean in those latitudes is due to currents, 
we cannot tell how much the removal of the sea would lower 
the absolute temperature of those places. Were the sea re- 
moved, the continents in high latitudes would not simply lose 
the heating advantages which they presently derive from the 
mere fact of their proximity to so much sea, but the removal 
would, in addition to this, deprive them of an enormous amount 
of heat which they at present receive from the tropics by means 
of ocean-currents. And, on the other hand, at the equator, 
were the sea removed, the continents there would not simply 
lose the cooling influences which result from their proximity to 
so much water, but, in addition to this, they would have to 
endure the scorching effects which would result from the heat 
which is at present carried away from the tropics by ocean- 
currents. 

We have already seen that Professor Forbes concluded that 
the removal of the sea would raise the mean temperature of the 
equator 30^, and lower the temperature of the poles 28° ; it is 
therefore perfectly certain that, had he added to his result the 



DISTRIBUTION OF HEAT. 51 

effeot due to ocean-currents, and had he been aware that about 
one-fifth of all the heat possessed by the Atlantic is actually 
deriyed from the equator by means of the Gulf-stream, he would 
have assigned a temperature U\ the equator and the poles, of a 
globe all land, differing not very far from what I have concluded 
would be the temperature of those places were all ocean and 
aerial currents stopped, and each place to depend solely upon 
the heat which it received directly from the sun. 

Wiihout Oceau'CurrenU the Olobe tcould not be habitable. — All 
these foregoing considerations show to what an extent the 
climatic condition of our globe is due to the thermal influences 
of ocean-currents. 

Ab regards the northern hemisphere, we have two immense 
oceans, the Pacific and the Atlantic, extending from the equator 
to near the north pole, or perhaps to the pole altogether. 
Between these two oceans lie two great continents, the eastern 
and the western. Owing to the earth's spherical form, far too 
much heat is received at the equator and far too little at high 
latitudes to make the earth a suitable habitation for sentient 
beings. The function of these two great oceans is to remove 
the heat from the equator and carry it to temperate and polar 
regions. Aerial currents could not do this. They might 
remove the heat from the equator, but they could not, as we 
have already seen, carry it to the temperate and polar regions ; 
for the greater portion of the heat which aerial currents remove 
from the equator is dissipated into stellar space: the ocean 
alone can convey the heat to distant shores. But aerial currents 
have a most important function ; for of what avail would it be, 
though ocean-currents should carry heat to high latitudes, if 
there were no means of distributing the heat thus conveyed 
over the land P The function of aerial currents is to do this. 
Upon this twofold arrangement depends the thermal condition 
of the globe. Exclude the waters of the Pacific and the 
Atlantic from temperate and polar regions and place them at 
the equator, and nothing now existing on the globe could live 
in high latitudes. 



32 CLIMATE AND TIME. 

Were these two great oceans placed beside each other on one 
side of the globe, and the two great continents placed beside 
each other on the other side, the northern hemisphere would 
not then be suitable for the present order of things : the land 
on the central and on the eastern side of the united continent 
would be far too cold. 

The foregoing Conclusions not affected by the Imperfection of the 
Data. — The general results at which we have arrived in reference 
to the influence of ocean-currents on the climatic condition of 
the globe are not affected by the imperfection of the data 
employed. It is perfectly true that considerable uncertainty 
prevails regarding some of the data; but, after making the 
fullest allowance for every possible error, the influence of 
currents is so enormous that the general conclusion cannot be 
materially affected. I can hardly imagine that any one familiar 
with the physics of the subject will be likely to think that, 
owing to possible errors in the data, the effects have probably 
been doubled. Even admitting, however, that this were proved 
to be the case, still that would not materially alter the general 
conclusion at which we have arrived. The influence of ocean- 
currents in the distribution of heat over the surface of the 
globe would still be admittedly enormous, whether we concluded 
that owing to them the present temperature of the equator is 
65° or 27° colder than it would otherwise be, or the poles 83° 
or 41° hotter than they would be did no currents exist. 

Nay, more, suppose we should again halve the result ; even 
in that case we should have to admit that, owing to ocean- 
currents, the equator is about 14° colder and the poles about 21° 
hotter than they would otherwise be ; in other words, we should 
have to admit that, were it not for ocean-currents, the mean 
temperature of the equator would be about 100° and the mean 
temperature of the poles about — 21°. 

If the influence of ocean-currents in reducing the difference 
between the temperature of the equator and poles amounted to 
only a few degrees, it would of course be needless to put much 
weight on any results arrived at by the method of calculation 



DISTRIBUTION OF HEAT, 



53 



which I have adopted ; but when it is a matter of two hundred 
degrees^ it is not at all likely that the general results will be 
▼ery much affected by any errors which may ever be found in 
the data. 

Objections of a palaeontological nature have frequently been 
urged against the opinion that our island is much indebted for 
its mild climate to the influence of the Gulf-stream ; but, from 
what has already been stated, it must be apparent that all 
objections of that nature are of little avail. The palaeontologist 
may detect, from the character of the flora and fauna brought 
up from the sea-bottom by dredging and other means, the 
presence of a warm or of a cold current ; but this can never 
enable him to prove that the temperate and polar regions are 
not affected to an enormous extent by warm water conveyed 
from the equatorial regions. For anything that palaeontology 
can show to the contrary, were ocean-currents to cease, the 
mean annual temperature of our island might sink below the 
present mid-winter temperature of Siberia. What would be 
the thermal condition of our globe were there no ocean-currenti 
is a question for the physicist ; not for the naturalist 



CHAPTER IV. 

OUTLINE OF THE PHYSICAL AGENaES WTIICH LEAD TO SBCULAB 

CHANGES OF CLIMATE. 

Eocentricity of the Earth*8 Orbit ; its Effect on Climate. — Glacial Epoch not the 
direct Result of an Increase of Eccentricity. — An important CoiiaideratioQ 
overlooked. — Change of Eccentricity affectd Climate only indirectly.— 
Agencies which are brought into Operation by an Increase of Eccentricity. — 
How an Accumulation of Snow is produced. — The EtTect of Snow on the 
Summer Temperature. — Reason of tho low Summer Temperature of PoUr 
Regions. — Deflection of Ocoan-currents the chief Cause of secular Changes 
of Climate. — How tho foregoing Causes deflect Ocean -currents. — N«ame8t 
of the Sun in Perigee a Cause of the Accumulation of Ice. — A remarkable 
Circumstance regarding the Causes which leiid to secular Changes of Climate. 
— Tho primary Cause an Increase of Eccentricity. — M&m Temperature of 
whole Eaith should be greater in Aphelion than iu Poriholiun. — Professor 
Tyndall on the Glacial Epoch. — A general Re<luction of Temperature will 
not produce a Glacial Epoch. — Objection from tho present Condition of the 
Planet Mers. 

Prinmn/ cause of Change of Eccentricity of the EartVz Orbit. 
— There are two causes affecting the positioD of the earth in 
relation to the sun, which must, to a very large extent, influence 
the earth's climate ; viz., the precession of the equinoxes and 
the change in the eccentricity of the earth's orbit. If we duly 
examine the combined influence of these two causes, we shall 
find that the northern and southern portions of the globe are 
subject to an excessively slow seciJar change of climate, con- 
sisting in a slow periodic change of alternate warmer and colder 
cycles. 

According to the calculations of Leverrier, the superior limit 
of the earth's eccentricity is 0-07775.* The eccentricity is at 

* Connaitsance des Ttmpi for 18 f 8 (Additions). Lagrange's determination 
makes tUe superior limit 007641 (Memoirs of the Berlin Aciideniy ibr 1782, 
p. 273). Recently the laborious task of re-investigating the whole subject of the 
•ecalar wiAtiona of the elementd of the planetnry orbits was undertaken by Mr. 



PHYSICAL AGENCIES, 55 

present diminiahing, and will continue to do so during 23,980 
years, from the year 1800 a.d., when its value will be then 
•003314. 

The change in the eccentricity of the earth's orbit may affect 
the climate in two different ways; viz., by either increasing 
or diminishing the mean annual amount of heat received from 
the sun, or by increasing or diminishing the difference between 
summer and winter temperature. 

Let us consider the former case first. The total quantity of 
heat received from the sun during one revolution is inversely 
proportional to the minor axis. 

The difference of the minor axis of the orbit when at its 
maximum and its minimum state of eccentricity is as 997 to 
1000. This small amount of difference cannot therefore sensibly 
affect the climate. Hence we must seek for our cause in the 
second case under consideration. 

There is of course as yet some little uncertainty in regard to 
the exact mean distance of the sun. I shall, however, in the 
present volume assume it to be 91,400,000 miles. When the 
eccentricity is at its superior limit, the distance of the sun from 
the earth, when the latter is in the aphelion of its orbit, is no 
less than 98,506,350 miles ; and when in the perihelion it is 
only 84,293,650 miles. The earth is therefore 14,212,700 miles 
further from the sun in the former position than in the latter. Tlie 
direct heat of the sun being inversely as the square of the dis- 
tance, it follows that the amount of heat received by the earth 
when in these two positions will be as 19 to 26. Taking the 
present eccentricity to be '0168, the earth's distance during 
winter, when nearest to the sun, is 89,864,480 miles. Suppose 
now that, according to the precession of the equinoxes, winter in 
our northern hemisphere should happen when the earth is in 

Stockwell, of the United States. Ho han taken into account the dii»tiirhing in* 
fluence of the planet Neptune, tho existence of wiiich was not knowa when 
Lev^rier's computations were made ; and ho finds that the ecentriciiy of ihe 
earth's orbit will always be included within the limits of and 0'0t>U3S88. Mr. 
SU'Ckweirs elaborate Memoir, extending over no fewer than two hundred pages, 
will be found in the eighteenth volume of the '* Smithsonian Contributions tc 
Knowledge.'* 

4 



56 CLIMATE AND TIME. 

the aphelion of its orbit, at the time when the orbit is ut its 
greatest eccentricity ; the earth would then be 8,641,870 miles 
fiirther from the sun in winter than at present. The direct 
heat of the sun would therefore be one-fifth less during that 
season than at present ; and in summer one-fifth greater. This 
enormous difference would affect the climate to a very great 
extent. But if winter under these circumstances should happen 
when the earth is in the perihehon of its orbit, the earth would 
then bo 14,212,700 miles nearer the sun in winter than in 
summer. In this case the difference between winter and sum- 
mer in the latitude of this country would be almost annihilated. 
But as the winter in the one hemisphere corresponds with the 
summer in the other, it follows that while the one hemisphere 
would be enduring the greatest extremes of summer heat and 
winter cold, the other would be enjoying a perpetual summer. 

It is quite true that whatever may be the eccentricity of the 
earth's orbit, the two hemispheres must receive equal quantities 
of heat per annum ; for proximity to the sun is exactly com- 
pensated by the effect of swifter motion — the total amount of 
heat received from the sun between the two equinoxes is the 
same in both halves of the year, whatever the eccentricity of 
the earth's orbit may be. For exauiple, whatever extra heat 
the southern hemisphere may at present receive from the sun 
during it^ summer months owing to greater proximity to the 
sun, is exactly compensated by a corresponding loss arising from 
the shortness of the season ; and, on the other hand, whatever 
deficiency of heat we in the northern hemisphere may at present 
have during our summer half year in consequence of the earth's 
distance from the sun, is also exactly compensated by a corre- 
sponding length of season. 

It has been shown in the introductory chapter that a simple 
change in the sun's distance would not alone produce a glacial 
epoch, and that those physicists who confined their attention 
to purely astronomical effects were perfectly correct in affirming 
that no increase of eccentricity of the earth's orbit could account 
for that epoch. But the important fact was overlooked that 



PHYSICAL AGENCIES, 57 

although the ghicial epoch could not result directly from un 
increase of eccentricity, it might nevertheless do so indirectly. 
The glacial epoch, as I hope to show, was not due directly to an 
increase in the eccentricity of the earth's orbit, but to a number 
of physical agents that were brought into operation as a result 
of an increase. 

I shall now proceed to give an outline of what these physical 
agents were, how they were brought into operation, and the 
way in which they led to the glacial epoch. 

When the eccentricity is about its sui)erior limit, the com- 
bined effect of all those causes to which I allude is to lower to a 
very great extent the temperature of the hemisphere whose 
winters occur in aphelion, and to raise to nearly as great an 
extent the temperature of the opposite hemisphere, where winter 
of course occurs in perihelion. 

With the eccentricity at its superior limit and the winter 
occurring in the aphelion, the esirth would bo 8,641,870 miles 
further from the sun during that season than at present. The 
reduction in the amount of heat received from the sun owing 
to his increased distance would, upon the principle we have 
stated in Chapter II., lower the midwinter temperature to an 
enormous extent. In temperate regions the greater portion of 
the moisture of the air is at present precipitated in the form of 
rain, and the very small portion which falls as snow disappears 
in the course of a few weeks at most. But in the circumstances 
under consideration, the mean winter temperature would be 
lowered so much below the freezing-point that what now falls 
as rain during that season would then fall as snow. This is not 
all ; the winters would then not only be colder than now, but 
they would also be much longer. At present the winters ai'e 
nearly eight days shorter than the summers; but with tlie 
eccentricity at its superior limit and the winter solstice in 
aphelion, the length of the winters would exceed that ot* the 
simimers by no fewer than thirty-six days. The lowering of 
the temperature and the lengthening of the winter would both 
tend to the same effect, viz., to increase the amount of snow 



58 CLIMATE AND TIME. 

accumulated during the winter ; for, other things being equals 
the Lirger the snow-accumulating period the greater the accu- 
mulation. I may remark, however, that the absolute quantity 
of heat received during winter is not affected bj the decrease 
in the 8un*8 heat,* for the additional length of the season 
compensates for this decrease. As regards the absolute amount 
of heat received, increase of the sun's distance and lengthening 
of the winter are compensatory, but not so in regard to the 
amount of snow accumulated. 

The consequence of this state of things would be that, at the 
commencement of the short summer, the ground would be 
covered with the winter's accumulation of snow. 

Again, the presence of so much snow would lower the summer 
temperiiture, and prevent to a great extent the melting of the 
snow. 

There are three separate ways whereby accumulated masses 
of snow and ice tend to lower the summer temperature, viz. : — 

¥ird. By means of direct radiation. No matter what the 
intensity of the sun's rays may be, the temperature of snow and 
ice can never rise above 32°. Hence the presence of snow and 
ice tends by direct radiation to lower the temperature of all 
surrounding bodies to 32°. 

In Greenland, a country covered with snow and ice, the 
pitch has been seen to melt on the side of a ship exposed to the 
direct rays of the sun, while at the same time the surrounding 
air was far below the freezing-point ; a thermometer exposed to 
tlie direct radiation of the sun has been observed to stand above 
100°, while the air surrounding the instrument was actually 
12° below the freezing-point, t A similar experience has been 
recorded by travellers on the snow-fields of the Alps. J 

These results, surprising as they no doubt appear, are K'hat 

• Whi n tho eccentricity is at its superior limit, the Mbsolute q\ antitj* of heat 
rt'crivttl I'V the earth dining the year is, however, about one three- )iundredth 
part ^Tt^attr than at present. But this does not affect the question at issue. 

t Scoitsby's *' Arctic lUgious," vol. u.. p. 379. Diiniell's ** 3leteorologjr,* 
vol. ii., p. 123. 

X Tyudull, *'0n Heat," arlicle 364. 



PHYSICAL AGENCIES. 59 

we ought to expect under the circamstances. The diather- 
mancy of air has been well established by the researches of 
Professor Tyndall on radiant heat. Perfectly dry air seems to 
be nearly incapable of absorbing radiant heat. The entire 
radiation passes through it almost without any sensible absorp- 
tion. Consequently the pitch on the side of the ship may be 
melted, or the bulb of the thermometer raised to a high tem- 
perature by the direct rays of the sun, while the surrounding 
air remains intensely cold. " A joint of meat," says Professor 
Tyndall, "might be roasted before a fire, the air around the 
joint being cold as ice." * The air is cooled by contact with 
the snow-covered ground, but is not heated by the radiation 
from the sun. 

When the air is humid and charged with aqueous vapour, a 
similar cooling effect also takes place, but in a sb'ghtly different 
way. Air charged with aqueous vapour is a good absorber of 
radiant heat, but it can only absorb those rays which agree with 
it in period. It so happens that rays from snow and ice are, of 
all others, those which it absorbs best. The humid air will 
absorb the total radiation from the snow and ice, but it will 
allow the greater part of, if not nearly all, the sun's rays to 
pass unabsorbcd. But during the day, when the sun is shining, 
the radiation from the snow and ice to the air is negative ; that 
is, the snow and ice cool the air by radiation. The result is, 
the air is cooled by radiation from the snow and ice (or rather, 
we should say, to the snow and ice) more rapidly than it is 
heated by the sun ; and, as a consequence, in a country like 
Greenland, covered with an icy mantle, the temperature of the 
air, even during summer, seldom rises above the freezing-point. 
Snow is a good reflector, but as simple reflection does not 
change the character of the rays they would not be absorbed 
by the air, but would pass into stellar space. 

Were it not for the ice, the summers of North Greenland, 
owing to the continuance of the sun above the horizon, would 
be as warm as those of England ; but, instead of this, the 

• Tyndall, *' On Heat," article 364. 



60 CLIMA TE AND TIME. 

Greenland summers are colder than our winters. Cover India 
with an ice sheet, and its summers would be colder than those 
of England. 

Second. Another cause of the cooling effect is that the rays 
which fall on snow and ice are to a great extent reflected back 
into space.* But those that are not reflected, but absorbed, do 
not raise the temperature, for they disappear in the mechanical 
work of melting the ice. The latent heat of ice is about 
142° F. ; consequently in the melting of every pound of ice a 
quantity of heat sufficient to raise one pound of water 142° dis- 
appears, and is completely lost, so far as temperature is con- 
cerned. This quantity of heat is consumed, not in raising the 
temperature of the ice, but in the mechanical work of tearing 
the molecules separate against the forces of cohesion binding 
them together into the solid form. No matter what the inten- 
sity of the sun's heat may be, the surface of the ground will 
remain permanently at 32° so long as the snow and ice con 
tinue unmelted. 

Third. Snow and ice lower the temperature by chilling the 
air and condensing the vapour into thick fogs. The great 
strength of the sun's rays during summer, due to his nearness 
at that season, would, in the first place, tend to produce an 
increased amount of evaporation. But the presence of snow- 
clad mountains and an icy sea would chill the atmosphere and 
condense the vapour into thick fogs. The thick fogs and 
cloudy sky would effectually prevent the sun's rays from reach- 
ing the earth, and the snow, in consequence, would remain un- 
melted during the entire summer. In fact, we have this very 
condition of things exemplified in some of the islands of the 
Southern Ocean at the present day. Sandwich Land, which 
is in the same parallel of latitude as the north of Scotland, 
is covered vdih. ice and snow the entire summer ; and in the 
island of South Georgia, which is in the same parallel as the 
centre of England, the perpetual snow descends to the very 
sea-beach. The following is Captain Cook's description of this 
dismal place: — " We thought it very extraordinary," he saysi 

• See Phil. Mag., March, 1870. p. 



PHYSICAL AGENCIES. 61 

*' that an island between the latitudes of 54^ and 55^ should, in 
the very height of summer^ be ahnost wholly covered with 

frozen snow, in some places many fathoms deep The 

head of the bay was terminated by ice-cHffs of considerable 
height ; pieces of which were continually breaking off, which 
made a noise like a cannon. Nor were the interior parts of the 
country less horrible. The savage rocks raised their lofty 
summits till lost in the clouds, and valleys were covered with 
seemingly perpetual snow. Not a tree nor a shrub of any size 
were to be seen. The only signs of vegetation were a strong- 
bladed gross growing in tufts, wild bumet, and a plant-like 

moss seen on the rocks We are inclined to think that 

the interior parts, on account of their elevation, never enjoy 
heat enough to melt the snow in such quantities as to produce 
a river, nor did we find even a stream of fresh water on the 
whole coast."* 

Captain Sir James Ross found the perpetual snow at the sea- 
level at Admiralty Inlet, South Shetland, in lat. 64° ; and while 
near this place the thermometer in the very middle of summer 
fell at night to 23° F. ; and so rapidly was the yoimg ice forming 
around the ship that he began, he says, " to have serious appre- 
hensions of the ships being frozen in." t At the comparatively 
low latitude of 59° S., in long. 171° E. (the corresponding lati- 
tude of our Orkney Islands), snow was falling on the longest 
day, and the surface of the sea at 32°. iT And during the month 
of February (the month corresponding to August in our hemi- 
sphere) there were only three days in which they were not 
assailed by snow-showers. § 

In the Straits of Magellan, in 63° S. lat., where the direct 
heat of the sun ought to be as great as in the centre of England, 
MM. Churrca and Galcano have seen snow fall in the middle of 
summer; and though the day was eighteen hours long, the 
thermometer seldom rose above 42° or 44°, and never above 
61°.|| 

• Captain Ccxjk'B " Second VoyuHP," vol. ii., pp. 232, 235. 
t " Antarctic Regions," vol. ii., pp. 346—349. 
} Ibid., vol. i., p. 167. k Ibid., vol. ii., p. 862. 

I Edinborgrh Philosophirnl Journ:il. vol. iv.. p. 260. 



t>2 CLIMATE AND TIME. 

This rigorous condition of climat© chiefly results from the 
rays of the sun being intercepted by the dense fogs which 
envelope those regions during the entire summer ; and the fogs 
again are due to the air being chilled by the presence of the 
snow- clad mountains and the immense masses of floating ice 
which come from the antarctic seas. The reduction of the sun's 
heat and lengthening of the winter, which would take place 
when the eccentricity is near to its superior limit and the 
winter in aphelion, would in this country produce a state of 
things perhaps as bad as, if not worse than, that which at pre- 
sent exists in South Georgia and South Shetland. 

If we turn our attention to the polar regions, we shall find 
that the cooling efiects of snow and ice are even still more 
marked. The coldness of the summers in polar regions is owing 
almost solely to this cause. Captain Scoresby states that, in 
regard to the arctic regions, the general obscurity of the atmo- 
sphere arising from fogs or clouds is such that the sun is fre- 
quently invisible during several successive days. At such 
times, when the sun is near the northern tropic, there is scarcely 
any sensible quantity of light from noon till midnight.* " And 
snow," he says, "is so common in the arctic regions, that it 
may be boldly stated that in nine days out of ten during the 
months of April, May, and June more or less falls." t 

On the north side of Hudson's Bay, for example, where the 
quantity of floating ice during summer is enormous, and dense 
fogs prevail, the mean temperature of June does not rise above 
the freezing-point, being actually 13°'5 below the normal tem- 
perature ; while in some parts of Asia under the same latitude, 
where there is comparatively little ice, the mean temperature of 
June is as high as 60°. 

The mean temperature of Van Rensselaer Harbour, in lat. 
78° 37' N., long. 70° 53' TV., was accurately determined from 
hourly observations made day and night over a period of two 
years by Dr. Kane. It was found to be as follows : — 

* Scor«8by'8 "Arctic Regions," vol. i., p. 378. f Ibid., p. 42/». 



PHYSICAL AGENCIES, 63 

Winter -28-69 

Spring -10-59 

Summer 4~93*38 

Auinmn — 4*03 

But althoagb the quantity of heat received from the sun at that 
latitude ought to have been greater during the summer than in 
England,* yet nevertheless the temperature is only l°-38 above 
the freezing-point. 

The temperature of Port Bowen, lat. 73° 14' N., was found 
to be as follows : — 



n 



Winter -2609 

Spring — 6-77 

Summer +34*40 

Autumn 4-^0*68 

Here the summer is only 2^*4 above the freezing-point. 

The condition of things in the antarctic regions is even still 
worse than in the arctic. Captain Sir James Ross, when be- 
tween lat. 66° S. and 77° 5' S., during the months of January 
and February, 1841, found the mean temperature to be only 
26°'5 ; and there were only two days when it rose even to the 
freezing-point. When near the ice-barrier on the 8th of 
February, 1841, a season of the year equivalent to August in 
England^ he had the thermometer at 12*^ at noon ; and so rapidly 
was the young ice forming around the ships, that it was with 
difficulty that he escaped being frozen in for the winter. 
" Three days later," he says, ** the thick falling snow prevented 
our seeing to any distance before us ; the waves as they broke 
over the ships froze as they fell on the decks and rigging, and 
covered our clothes with a thick coating of ice." t On visiting 
the barrier next year about the same season, he again ran the 
risk of being frozen in. He states that the surface of the sea 
presented one unbroken sheet of young ice as far as the eye 
could discover from the masthead. 

Lieutenant Wilkes, of the American Exploring Expedition, 
nays that the temperature they experienced in the antarctic re- 

• See Meech*ii memoir " On the Intensity of the Sun's Heiit and Light," 
** Smithsonian Contributions/' vol. ix. 
t " Antarctic Regions," vol. i., p. 240. 



i4 CUM ATE AND TIME. 

gions surprised bim, for they seldom, if ever, had it above 30°, even 
at midday. Captain Nares, when in Lititude 64" S., between the 
13th and 25th Februarr last (1674), found the mean temperatare 
of the air to be 31^*5 ; a lower temperature than \% met with 
in the arctic regions, in August, ten degrees nearer the pole.* 

These extraordinarilT low temperatures during summer, 
which we have just been detailing, were due solely to the 
presence of snow and ice. In South Georgia, Sandnich Land, 
and some other places which we have noticed, the summers 
ought to be about as warm as those of England ; vet to such an 
extent is the air cooled by means of floating ice coming from 
the antarctic regions, and the rays of the sun enfeebled by the 
dense fogs which prevail, that there is actually not heat suffi- 
cient even in the verv middle of summer to melt the snow 
lying on the sea-beach. 

We read with astonishment that a coimtrv in the latitude of 
Ensrland should in the very middle of summer be covered with 
snow down to the sea-shore — the thermometer seldom rising 
much above the freezing-point. But we do not consider it so 
surprising that the summer temperature of the polar regions 
should be low, for we are accustomed to regard a low tempera- 
ture as the normal condition of things there. TTe are, however, 
mistaken if we suppose that tho influence of ice on climate is 
less marked at the poles than at such places as South Georgia 
or Sandwich Land. 

It is true that a low summer temperature is the normal state 
of matters in very high latitudes, but it is so only in consequence 
of the perpetual presence of snow and ice. When we speak of 
the normal temperature of a place we mean, of course, as we 
have already seen, the normal temperature under the present 
condition of things. But were the ice removed from those 
regions, our present Tables of normal summer temperature 
would bo valueless. These Tables give us the normal June 
temperature while the ice remains, but they do not afford ns 
the least idea as to what that temperature would be were the 

• ChiUmger Beporta, No. 2, p. 10. 




PHYSICAL AGENCIES. 



6S 



ice removed. The mere removal of the ice, all things else 
remaining the same, would raise the summer temperature 
enormously. The actual June temperature of Melville Island, 
for example, is 37°, and Port Franklin, Nova Zembla, 36°-5 ; 
but were the ice removed from the arctic regions, we should 
then find that the summer temperature of those places would be 
about as high as that of England. This will be evident from 
the following considerations : — 

The temperature of a place, other things being equal, is pro- 
portionate to the quantity of heat received from the sun. If 
Greenland receives per given surface as much heat from the 
sun as England, its temperature ought to be as high as that of 
England. Now, from May 10 till August 3, a period of eighty- 
five days, the quantity of heat received from the sun in conse- 
quence of his remaining above the horizon is actually greater 
at the north pole than at the equator. 

Column II. of the following Table, calciJated by Mr. Meech,* 
represents the quantity of heat received from the sun on the 
15th of June at every lif of latitude. To simplify the Table, 
I have taken 100 as the unit quantity received at the equator 
on that day instead of the unit adopted by Mr. Meech : — 





L 


n. 


m. 




Ltttltnde. 


Qoantityof 


June 




hMt. 


tempeiutim. 


Equator .... 


e 




100 


800 




10 


111 


8M 




20 


118 


81-1 




30 


123 


77-3 




40 


125 


68-0 




50 


125 


58-8 




60 


123 


51-4 




70 


127 


39-2 




80 


133 


30-2 


North Pole . . 


90 


136 


27-4 



The calculations are, of course, made upon the supposition 
that the quantity of rays cut off in passing through the atmo- 

• See " Smithsonian Contributions " toI. it. 



50 CLIMATE AND TIME, 

Bphero IS the same at the poles as at the equator, which, as we 
know, is not exactly the case. But, notwithstanding the extra 
loss of solar heat in high latitudes caused by the greater amount 
of rays that are cut oflf, still, if the temperature of the arctic 
summers were at all proportionate to the quantity of heat 
received from the sun, it ought to be very much higher than it 
actually is. Column III. represents the actual mean June 
temperature, according to Prof. Dove, at the corresponding 
latitudes. A comparison of these two columns will show the 
very great deficiency of temperature in high latitudes during 
summer. At the equator, for example, the quantity of heat 
received is represented by 100 and the temperature 80° ; while 
at the pole the temperature is only 27°'4, although the amount 
of heat received is 136. This low temperature during summer, 
from what has been already shown, is due chiefly to the presence 
of snow and ice. If by some means or other we could remove 
the snow and ice from the arctic regions, they would then enjoy a 
temperate, if not a hot, summer. In Greenland, as we have already 
seen, snow falls even in the very middle of summer, more or less, 
nine days out of ten ; but remove the snow from the northern 
hemisphere, and a snow-shower in Greenland during summer 
would be as great a rarity as it would be on the plains of India. 

Other things being equal, the quantity of solar heat received 
in Greenland during summer is considerably greater than in 
England. Consequently, were it not for snow and ice, it would 
enjoy as warm a climate during summer as that of England. 
Conversely, let the polar snow and ice extend to the latitude of 
England, and the summers of that country would be as cold as 
those of Greenland. Our summers would then be as cold as 
our winters are at present, and snow in the very middle of 
summer would perhaps be as common as rain. 

Mr, Mitrphifs Theory, — In a paper read before the Geological 
Society by Mr. Murphy* he admits that the glacial climate was 
due to an increase of eccentricity, but maintains in opposition 
to me that the glaciated hemisphere must be that in which the 

• Quart. Joum. GJeol. Soc., vol. xxv., p. 350. 



PHYSICAL AGENCIES. 67 

9umn;er occurs in aphelion during the greatest eccentricity of 
the eartVs orbit. 

I fear that Mr. Murphy must be resting his theory on the 
mistaken idea that a summer in aphelion ought to melt less 
snow and ice than one in perihelion. It is quite true that the 
longer summer in aphelion — other things being equal — is 
colder than the shorter one in perihelion, but the quantity 
of heat received from the sun is the same in both cases. Con- 
sequently the quantity of snow and ice melted ought also to be 
the same; for the amount melted is in proportion to the 
quantity of energy in the form of heat received. 

It is true that with us at present less snow and ice are melted 
during a cold summer than during a warm one. But this is 
not a case in point, for during a cold summer we have less heat 
than during a warm summer, the length of both being the 
same. The coldness of the summers in this case is owing 
chiefly to a portion of the heat which we ought to receive from 
the sun being cut off by some obstructing cause. 

The reason why we have so little snow, and consequently so 
little ice, in temperate regions, is not, as Mr. Murphy seems to 
suppose, that the heat of summer melts it all, but that there is so 
little to melt. And the reason why we have so little to melt is 
that, owing to the warmth of our winters, we have generally rain 
instead of snow. But if you increase the eccentricity very much, 
and place the winter in perihelion, we should probably have no 
snow whatever, and, as far as glaciation is concerned, it would 
then matter very little what sort of summer we had. 

But it is not correct to say that the perihelion summer of the 
glacial epoch must have been hot. There are physical reasons, 
as we have just seen, which go to prove that, notwithstand- 
ing the nearness of the sun at that season, the temperature 
would seldom, if ever, rise much above the freezing-point. 

Besides, Mr. Murphy overlooks the fact that the nearness of 
the sun during summer was nearly as essential to the production 
of the ice, as we shall shortly see, as his great distance during 
winter. 



68 CLIMATE AND TIME 

We must now proceed to the consideration of an agency 
wliich is brought into operation by the foregoing condition of 
things^ an agency far more potent than any which has yet 
come under our notice, viz., the Deflection of* Ocean-currents. 

Deflection of Ocean-currents the chief Cause of secular Changes 
of Climate. — The enormous extent to which the thermal con- 
dition of the globe is affected by ocean-currents seems to cast 
new light on the mystery of geological climate. What, for 
example, would be the condition of Europe were the Gulf- 
stream stopped, and the Atlantic thus deprived of one-fifth 
of the absolute amount of heat which it is now receiving above 
what it has in virtue of the temperature of space? K the 
results just arrived at be at all justifiable, it follows that the 
stoppage of the stream would lower the temperature of northern 
Europe to an extent that would induce a condition of climate 
as severe as that of North Greenland; and were the warm 
currents of the North Pacific also at the same time to be 
stopped, the northern hemisphere would assuredly be subjected 
to a state of general glaciation. 

Suppose also that the warm currents, having been withdrawn 
from the northern hemisphere, should flow into the Southern 
Ocean : what then would be the condition of the southern 
hemisphere? Such a transference of heat would raise the 
temperature of the latter hemisphere about as much as it 
would lower the temperature of the former. It would conse- 
quently raise the mean temperature of the antarctic regions 
much above the freezing-point, and the ice under which those 
regions are at present buried would, to a great extent at least, 
disappear. The northern hemisphere, thus deprived of the 
heat from the equator, would be under a condition of things 
similar to that which prevailed during the glacial epoch; 
while the other hemisphere, receiving the heat from the 
equator, would be under a condition of climate similar to what 
we know prevailed in the northern hemisphere during a part 
of the Upper Miocene period, when North Greenland enjoyed 
a climate as mild as that of England at the present day. 



PHYSICAL AGENCIES. 69 

This is LO mere picture of the imagination, no mere hypo* 
thesis deyised to meet a difficult case ; for if what has already 
been stated be not completely erroneous, all this follows as a 
necessary consequence from physical principles. If the warm cur- 
rents of the equatorial regions be all deflected into one hemisphere, 
such must be the condition of things. How then do the agencies 
which we have been considering deflect ocean-currents ? 

Sow the foregoing Causes deflect Ocean-currents, — A high 
condition of eccentricity tends, we have seen, to produce an 
accumulation of snow and ice on the hemisphere whose winters 
occur in aphelion. This accumulation tends in turn to lower 
the summer temperature, to cut off the sun's rays, and so 
to retard the melting of t£e snow. In short, it tends to pro- 
duce on that hemisphere a state of glaciation. Exactly opposite 
effects take place on the other hemisphere, which has its winter 
in perihelion. There the shortness of the winters and the high- 
ness of the temperature, owing to the sun's nearness, combine to 
prevent the accimiulation of snow. The general result is that 
the one hemisphere is cooled and the other heated. This state of 
things now brings into play the agencies which lead to the 
deflection of the Gulf-stream and other great ocean-currents. 

Owing to the great difference between the temperature of 
the equator and the poles, there is a constant flow of air from 
the poles to the equator. It is to this that the trade-winds owe 
their existence. Now as the strength of these winds, as a 
general rule, will depend upon the difference of temperature that 
may exist between the equator and higher latitudes, it follows 
that the trades on the cold hemisphere will be stronger than 
those on the warm. When the polar and temperate regions of 
the one hemisphere are covered to a Large extent with snow and 
ice, the air, as we have just seen, is kept almost at the freezing- 
point during both summer and winter. The trades on that 
hemisphere will, of necessity, be exceedingly powerful ; while 
on the other hemisphere, where there is comparatively little 
snow and ice, and the air is warm, the trades will, as a conse- 
quence, be weak. Suppose now the northern hemisphere to be 



70 CLIMATE AND TIME. 

the cold one. The north-east trade-winds of this hemisphere, 
will far exceed in strength the south-east trade-winds of the 
southern hemisphere. The median-line between the trades will 
consequently lie to a very considerable distance to the south of 
the equator. We have a good example of this at the present 
day. The diflFerence of temperature between the two hemi- 
spheres at present is but trifling to what it would be in the case 
under consideration ; yet we find that the south-east trades of 
the Atlantic blow with greater force than the north-east trades, 
and the result is that the south-east trades sometimes extend to 
10° or 15° N. lat., whereas the north-east trades seldom blow 
south of the equator. The effect of the northern trades blowing 
across the equator to a great distance will be to impel the warm 
water of the tropics over into the Southern Ocean. But this is 
not all ; not only would the median-line of the trades be shifted 
southwards, but the great equatorial currents of the globe 
would also be shifted southwards. 

Let us now consider how this would affect the Gulf -stream. 
The South American continent is shaped somewhat in the form 
of a triangle, with one of its angular comers, called Cape St. 
Roque, pointing eastwards. The equatorial current of the 
Atlantic impinges against this corner ; but as the greater portion 
of the current lies a little to the north of the comer, it flows 
westward into the Gulf of Mexico and forms the Gulf-stream. 
A considerable portion of the water, however, strikes the land 
to the south of the Cape and is deflected along the shores of 
Brazil into the Southern Ocean, forming what is known as the 
Brazilian current. 

Now it is perfectly obvious that the shifting of the equatorial 
current of the Atlantic only a few degrees to the south of its 
present position — a thing which would certainly take place 
under the conditions which we have been detailing — would 
turn the entire current into the Brazilian branch, and instead 
of flowing chiefly into the Gulf of Mexico as at present, it 
would all flow into the Southern Ocean, and the Gulf-stream 
would ccnwequently be stopped. The stoppage of the Gulf 



PHYSICAL AGENCIES, 71 

stream^ combined with all those causes whicli we have just been 
considering, would place Europe under glacial conditions; 
while, at the same time, the temperature of the Southern Oceaii 
would, in consequence of the enormous quantity of warm water 
received, have its temperature (already high from other causes) 
riiised enormously. 

Deflection of the Gulf-stream during the Glacial Epoch indicated 
by the Difference heticeen the Clyde and Canadian Shell-beds. — That 
the glaciation of north-western Europe resulted to a great 
extent from the stoppage of the Gulf-stream may, I think, be 
inferred from a circumstance pointed out by the Rev. Mr. 
Crosskey, several years ago, in a paper read before the Glasgow 
Geological Society.* He showed that the diflFerence between 
the glacial shells of Canada and those now existing in the Gulf 
of St. Lawrence is much less marked than the difference between 
the glacial shells of the Clyde beds and those now existing in 
the Firth. And from this he justly infers that the change of 
climate in Canada since the glacial epoch has been fur less 
complete than in Scotland. 

The return of the Gulf-stream has raised the mean annual 
temperature of our island no less than 15° above the normal, 
while Canada, deprived of its influence and exposed to a cold 
stream from polar regions, has been kept nearly n8 much below 
the normal. 

Let us compare the present temperature of the two countries. 
In making our comparison we must, of course, compare places 
on the same latitude. It will not do, for example, to compare 
Glasgow with Montreal or Quebec, places on the latitude of the 
south of France and north of Italy. It will be found that the 
difference of temperature between the two countries is so enor- 
mous as to appear scarcely credible to those who have not 
examined the matter. The temperatures have all been taken 
from Professor Dove's work on the " Distribution of Heat over 
the Surface of the Globe," and his Tables published in tbf 
Report of the British Association for 1847. 

• Trans, of Glasgow Gool. Soc. for 1866. 



;a CLIMATE AND TIME. 

The mean temperature of Scotland for January is about 
38° F., while in some parts of Labnidor, on the same latitude, 
and all along the central parts of North America lying to the 
north of Upper Canada, it is actually 10°, and in many places 
13° below zero. The January temperature at the Cumberland 
House, which is situated on the latitude of the centre of 
England, is more than 13° below zero. Here is a difference 
of no less than 51°. The normal temperature for the month of 
January in the latitude of Glasgow, according to Professor 
Dove, is 10°. Consequently, owing to the influence of the 
Gulf-stream, we are 28° warmer during that month than we 
would otherwise be, while vast tracts of country in America are 
23° colder than they should be. 

The July temperature of Glasgow is Gl°, while on the same 
latitude in Labrador and places to the west it is only 49°. 
Glasgow during that month is 3° above the normal tempera* 
ture, while America, owing to the influence of the cold polar 
stream, is 9° below it. The mean annual temperature of 
Glasgow is nearly 50°, while in America, on the same latitude, 
it is only 30°, and in many places as low as 23°. The mean 
normal temperature for the whole year is 35°. Our mean 
annual temperature is therefore 15° above the normal, and that 
of America from 5° to 12° below it. The American winters are 
excessively cold, owing to the continental character of the 
climate, and the absence of any benefit from the Gulf-stream, 
while the summers, which would otherwise be warm, are, in 
the latitude of Glasgow, cooled down to a great extent by the 
cold ice from Greenland ; and the consequence is, that the 
mean annual temperature is about 20° or 27° below that of 
ours. The mean annual temperature of the Gulf of St. Law- 
rence is as low as that of Lapland or Iceland. It is no wonder, 
then, that the shells which flourished in Canada during the 
glacial epoch have not left the gulf and the neighbouring seas. 

TVe have good reason to believe that the climate of America 
during the glacial epoch was even then somewhat more severe 
ihan that of Western Europe, for the erratics of America extend 



.. _^. 



PHYSICAL AGENCIES. 73 

as far south as latitude 40^, while on the old continent they are 
not found much beyond latitude 50^. This difference may have 
resulted from the fact that the western side of a continent is 
always warmer than the eastern. 

In order to determine whether the cold was as great in 
America during the glacial epoch as in Western Europe, we 
must not compare the fossils found in the glacial beds about 
Montreal, for example, with those found in the Clyde beds, for 
Montreal lies much further to the south than the Clvde. The 
Clyde beds must be compared with those of Labrador, while 
the beds of Montreal must be compared with those of the south 
of France and the north of Italy, if any are to be found there. 

On the whole, it may be concluded that had the Oulf-stream 
not returned to our shores at the close of the glacial epoch, and 
had its place been supplied by a cold stream from the polar 
regions, similar to that which washes the shores of North 
America, it is highly probable that nearly every species found 
in our glacial beds would have had their representatives flourish- 
ing in the British seas at the present day. 

It is no doubt true that when we compare the places in 
which the Canadian shell-beds referred to by Mr. Crosskey 
are situated with places on the same latitude in Europe, the 
difference of climate resulting firom the influence of the Gulf- 
stream is not so great as between Scotland and those places 
which we have been considering ; but still the difference is 
sufficiently great to account for why the change of climate in 
Canada has been less complete than in Scotland. 

And what holds true in regard to the currents of the Atlantic 
holds also true, though perhaps not to the same extent, of the 
currents of the Pacific. 

Nearness of the Sun in Perigee a Cause of the Accumulation of 
Ice, — ^But there is still another cause which must be noticed : — 
A strong under current of air from the north implies an equally 
strong upper current to the north. Now if the effect of the 
under current would be to impel the warm water at the equator 
to the south, the effect of the upper current would be to carry 



74 CLIMATE AND TIME. 

the aqueous vapour formed at the equator to the north ; the 
upper current, on reaching the snow and ice of temperate 
regions, would deposit its moisture in the form of snow; so 
that, notwithstanding the great cold of the glacial epoch, it is 
probahle that the quantity of snow falling in the northern 
regions would be enormous. This would be particularly the 
case during summer, when the earth would be in the perihelion 
and the heat at the equator great. The equator woidd be the 
furnace where evaporation would take place, and the snow and 
ice of temperate regions would act as a condenser. 

Heat to produce evaporation is just as essential to the accu- 
mulation of snow and ice as cold to produce condensation. Now 
at Midsummer, on the supposition of the eccentricity being at 
its superior limit, the sun would be 8,641,870 miles nearer than 
at present during that season. The effect would be that the 
intensity of the sun's rays would be one-fifth greater than 
now. That is to say, for every five rays received by the ocean 
at present, six rays would be received then, consequently the 
evaporation during summer would be excessive. But the ice- 
covered land would condense the vapour into snow. It would, 
no doubt, be during summer that the greatest snowfall would 
take place. In fact, the nearness of the sun during that 
season was as essential to the production of the glacial epoch 
as was his distance during winter. 

The direct effect of eccentricity is to produce on one of the 
hemispheres a long and cold winter. This alone would not 
lead to a condition of things so severe as that which we know 
prevailed during the glacial epoch. But the snow and ice 
thus produced would bring into operation, as we have seen, a 
host of physical agencies whose combined efforts would be 
quite suflicient to do this. 

A remarkable Circumstance regarding those Causes ichich lead 
to Secular Changes of Climate. — There is one remarkable cir- 
cumstance connected with those physical causes which deserves 
special notice. They not only all lead to one result, viz., an 
accumulation of snow and ice, but they react on one another. 



PHYSICAL AGENCIES, 75 

It is quite a common thing in physics for the effect to react on 
the cause. In electricity and magnetism, for example, cause 
and effect in almost every case mutually act dnd react upon 
each other. But it is usually, if not universally, the case that 
the reaction of the effect tends to weaken the cause. The 
weakening influences of this reaction tend to impose a limit on 
the efficiency of the cause. But, strange to say, in regard to 
the physical causes concerned in the bringing about of the 
glacial condition of climate, cause and effect mutually reacted 
so as to strengthen each other. And this circumstance had a 
great deal to do with the extraordinary results produced. 

We have seen that the accumulation of snow and ice on the 
ground resulting from the long and coid winters tended to cool 
the air and produce fogs which cut off the sun's rays. The 
rays thus cut off diminished the melting power of the sun, and 
80 increased the accumulation. As the snow and ice continued 
to accumulate, more and more of the rays were cut off ; and on 
the other hand, as the rays continued to be cut off, the rate of 
accumulation increased, because the quantity of snow and ice 
melted became thus annually less and less. 

Again, during the long and dreary winters of the glacial 
epoch the earth would be radiating off its heat into space. Uad 
the heat thus lost simply gone to lower the temperature, the 
lowering of the temperature would have tended to diminish the 
rate of loss ; but the necessary result of this was the formation 
of snow and ice rather than the lowering of temperature. 

And, again, the formation of snow and ice facilitated the 
rate at which the earth lost its heat ; and on the other hand, 
the more rapidly the earth parted with its heat, the more 
rapidly were the snow and ice formed. 

Further, as the snow and ice accumulated on the one 
hemisphere, they at the same time continued to diminish on 
the other. This tended to increase the strength of the trade- 
winds on the cold hemisphere, and to weaken those on the 
warm. The effect of this on ocean currents would be to impel 
the warm water of the tropics more to the warm hemisphere 



/6 CLIMATE AND TIME, 

than to the cold. Suppose the northern hemisphere to be the 
cold one, then as the snow and ice began gradually to accumu- 
late there, the ocean currents of that hemisphere would begin 
to decrease in volume, while those on the southern, or warm, 
hemisphere, would pari passu increase. This withdrawal of 
heat from the northern hemisphere would tend, of course, to 
lower the temperature of that hemisphere and thus favour the 
accumulation of snow and ice. As the snow and ice accu- 
mulated the ocean currents would decrease, and, on the other 
hand, as the ocean currents diminished the snow and ice would 
accumulate, — the two eflFects mutually strengthening each other. 

The same must have held true in regard to aerial currents. 
The more the polar and temperate regions became covered with 
snow and ice, the stronger would become the trades and anti- 
trades of the hemisphere ; and the stronger those winds became, 
the greater would be the amount of moisture transferred from 
the tropical regions by the anti-trades to the temperate regions ; 
and on the other hand, the more moisture those winds brought 
to temperate regions, the greater would be the quantity of snow 
produced. 

The same process of mutual action and reaction would take 
place among the agencies in operation on the warm hemisphere, 
only the result produced would be diametrically opposite of that 
produced in the cold hemisphere. On this warm hemisphere 
action and reaction would tend to raise the mean temperature 
and diminish the quantity of snow and ice existing in temperate 
and poLvr regions. 

Had it been possible for each of those various physical agents 
which we have been considering to produce its direct eflFects 
without influencing the other agents or being influenced by 
them, its real efficiency in bringing about either the glacial 
condition of climate or the warm condition of climate would 
not have been so great. 

The primary cause that set all those various physical agencies 
in operation which brought about the glacial epoch, was a high 
state of eccentricity of the earth's orbit. When the eccentricity 



PHYSICAL AGENCIES^ 77 

18 at a high value, snow and ice begin to accumulate, owing to 
the increasing length and coldness of the winter on that hemi- 
sphere whose winter solstice is approaching toward the aphelion. 
The accumulating snow then begins to bring into operation all 
the various agencies which we have been describing ; and, as 
we have just seen, these, when once in fiill operation, mutually 
aid one another. As the eccentricity increases century by 
century, the temperate regions become more and more covered 
with snow and ice, first by reason of the continued incroase 
in the coldness and length of the winters, and secondly, and 
chiefly, owing to the continued increase in the potency of 
those physical agents which have been called into operation. 
This glacial state of things goes on at an increasing rate, and 
reaches a maximum when the solstice point arrives at the 
aphelion. After the solstice passes the aphelion, a contrary 
process commences. The snow and ice gradually begin to 
diminish on the cold hemisphere and to make their appearance 
on the other hemisphere. The glaciated hemisphere turns, 1 y 
degrees, warmer and the warm hemisphere colder, and this 
continues to go on for a period of ten or twelve thousand years, 
until the winter solstice reaches the perihelion. By this time 
the conditions of the two hemispheres have been reversed ; the 
formerly glaciated hemisphere has now become the warm one, 
and the warm hemisphere the glaciated. The transference of 
the ice from the one hemisphere to the other continues as long as 
the eccentricity remains at a high value. This will, perhaps, 
be better understood from an inspection of the frontispiece . 

The Mean Temperature of the whole Earth should be greater 
in Aphelion than in Perihelion, — When the eccentricity becomes 
reduced to about its present value, its influence on climate is 
but little felt. It is, however, probable that the present exten- 
sion of ice on the southern hemisphere may, to a considerable 
extent, be the result of eccentricity. The difibrence in the 
climatic conditions of the two hemispheres is just what should 
be according to theory : — (1) The mean temperature of that 
hemisphere is less than that of the northern. (2) The winters 



78 CLIMATE AND TIME. 

of the southern hemisphere are colder than those of the 
northern. (3) The summers, though occurring in perihelion, 
are also comparatively cold; this, as we have seen, is what 
ought to be according to theory. (4) The mean temperature 
of the whole earth is greater in June, when the earth is in 
aphelion, than in December, when it is in perihelion. This, I 
venture to affirm, is also what ought to follow according to 
theory, although this very fact has been adduced as a proof 
that eccentricity has at present but little eflFect on the climatic 
condition of our globe. 

That the mean temperature of the whole earth would, during 
the glacial epoch, be greater when the earth was in aphelion 
than when in perihelion will, I think, be apparent from the 
following considerations : — When the earth was in the peri- 
helion, the sun would be over the hemisphere nearly covered 
with snow and ice. The great strength of the sun's rays 
would in this case have little effect in raising the temperature ; 
it would be spent in melting the snow and ice. But when 
the earth was in the aphelion, the sun would be over the hemi- 
sphere comparatively free, or perhaps wholly free, from snow 
and ice. Consequently, though the intensity of the sun's rays 
would be less than when the earth was in perihelion, still it 
ought to have produced a higher temperature, because it would 
be chiefly employed in heating the ground and not consumed 
in melting snow and ice. 

Professor Tyndall on the Glacial Epoch, — " So natural," says 
Professor Tyndall, " was the association of ice and cold, that 
even celebrated men assumed that all that is needed to produce 
a great extension of our glaciers is a diminution of the sun's 
temperature. Had they gone through the foregoing reflections 
and calculations, they would probably have demanded m ore 
heat instead of less for the production of a glacial epoch. 
AVhat they really needed were condensers sufficiently powerful 
to congeal the vapour generated by the heat of the sun." 
{The Forms of Water, p. 154. Soe also, to the same effect, 
Heat Consklerefl as a Mode of Motion, chap, vi.) 



PHYSICAL AGENCIES. 79 

I do not know to whom Frofeasor Tyndall here refers, but 
eertainly hia remarks have no application to the theory nnder 
consideration, for according to it, as we have just seen, the ice 
of the glacial epoch was about as much due to the nearness of 
the sun in perigee as to his great distance in apogee. 

There is one theory, however, to which his remarks justly 
Apply, viz., the theory that the great changes of climate during 
geological ages resulted from the passage of our globe through 
different temperatures of space. What Professor Tyndall says 
shows plainly that the glacial epoch was not brought about by 
our earth passing through a cold part of space. A general 
reduction of temperature over the whole globe certainly would 
not produce a glacial epoch. Suppose the sun were ex- 
tinguished and our globe exposed to the temperature of 
stellar space (—239^ F.), this would certainly freeze the 
ocean solid from its surface to its bottom, but it would not 
cover the land with ice. 

Frofessor Tyndall's conclusions are, of course, equally con« 
elusive against Frofessor Balfour Stewart's theory, that the 
glacial epoch may have resulted from a general diminution in 
the intensity of the sun's heat. 

Nevertheless it would be in direct opposition to the well- 
established facts of geology to assume that the ice periods of 
the glacial epoch were warm periods. We are as certain from 
palseontological evidence that the celd was then much greater 
than now, as we are from physical evidence that the accumiila* 
tion of ice was greater than now. Our glacial shell-beds and 
remains of the mammoth, the reindeer, and musk-ox, teU of 
cold as truly as the markings on the rocks do of ice. 

Objection from the Present Condition of the Planet Mars. — It 
has been urged as an objection by Professor Charles Martins* 
and others, that if a high state of eccentricity could produce a 
glacial epoch, the planet Mars ought to be at present under 
a glacial condition. The eccentricity of its orbit amounts 
to 0*09322, and its southern winter solstice is, according to 

* lUvw det Deux Mondm for 1867. 
5 



8o CLIMATE AND TIME. 

Dr. Oudemans, of Batavia,* within 17° 41' 8" of aphelion. Con* 
sequently, it is supposed that one of the hemispheres should be 
in a glacial state and the other free from snow and ice. But it is 
believed that the snow accumulates around each pole during its 
winter and disappears to a great extent during its summer. 

There would be force in this objection were it maintained 
that eccentricity alone can produce a glacial condition of 
climate, but such is not the case, and there is no good ground 
for concluding that those physical agencies which led to the 
glacial epoch of our globe exist in the planet Mars. It is 
perfectly certain that either water must be different in con- 
stitution in that planet from what it is in our earth, or else its 
atmospheric envelope must be totally different from ours. For it 
is evident from what has been stated in Chapter II., that were 
our globe to be removed to the distance of Mars from the sun, 
the lowering of the temperature resulting from the decreaiie in 
the sun's heat would not only destroy every b'ving thing, but 
would convert the ocean into solid ice. 

But it must be observed that the eccentricity of Mars* orbit 
is at present far from its superior limit of 0*14224, and it may 
so happen in the economy of nature that when it approaches 
to that limit a glacial condition of things may supervene. 

The truth is, however, that very little seems to be known 
with certainty regarding the climatic condition of Mars. This 
is obvious from the fact that some astronomers believe that the 
planet possesses a dense atmosphere which protects it from 
cold ; while others maintain that its atmosphere is so exceed- 
ingly thin that its mean temperature is below the freezing- 
point. Some assert that the climatic condition of Mars re- 
sembles very much that of our earth, while others affirm that 
its seas are actually frozen solid to the bottom, and the poles 
severed with ice thirty or forty miles in thickness. For reasons 
which will be explained in the Appendix, Mars, notwith- 
standing its greater distance from the sun, may enjoy a climate 
as warm as that of our earth. 

* Letter to the author, Febroaiy, 1870. 



CHAPTER V. 

ftCASON WHY THE SOUTHERN HEMISPHERE IS COI.DKK THAK THV 

NORTHERN. 

Adh^mar's Explanation. — Adhtouu^s Theory founded upon a physical Mistako 
in regard to Radiation. — Professor J. D. Forbes on Underground Tempe- 
rature. — G^erally accepted Explanation. — Low Tempoiuture of Southern 
Hemisphere attrioutod to Prepondorance of Sea. — Heat transferred firom 
Southern to Northern Hemisphere by Ocean-current the true Explanation. 
— A large Portion of the Heat of the Gulf-stream derived from the Soutliem 
Hemisphere. 

Adhimar's Explanation, — It has long been known that on 
the southern hemisphere the temperature is lower and the 
accumulation of ice greater than on the northern. This 
difference has usually been attributed to the great preponder- 
ance of sea on the southern hemisphere. M. Adh^mar, on the 
other hand, attempts to explain this difference by referring it 
to the difference in the amount of beat lost by the two hemi- 
spheres in consequence of the difference of seven days in the 
length of their respective winters. As the northern winter is 
shorter than the summer, he concludes that there is an accu- 
mulation of heat on that hemisphere, while, on the other hand, 
the southern winter being longer than the summer, there is 
therefore a loss of heat on the southern hemisphere. " The 
south pole," he says, "loses in one year more heat than it 
receives, because the total duration of its night surpasses that 
of its day by 168 hours ; and the contrary takes place for the 
north pole. If, for example, we take for unity the mean 
quantity of heat which the sun sends off in one hour, the heat 
accumulated at the end of the year at the north pole will be 
expressed by 168, while the heat lost by the south pole will 



82 CLIMATE AND TIME. 

be equal to 168 timee what the radiation lessens it by in 
one hour, so that at the end of the year the difference in the 
heat of the two hemispheres will be represented by 336 times 
what the earth receives from the sun or loses in an hour by 
radiation."* 

Adh^mar supposes that about 10,000 years hence, when 
our northern winter will occur in aphelion and the southern 
in perihelion, the climatic conditions of the two hemispheres 
will be reversed ; the ice will melt at the south pole, and the 
northern hemisphere will become enveloped in one continnona 
mass of ice, leagues in thickness, extending down to temperate 
regions. 

This theory seems to be based upon an erroneous interpreta- 
tion of a principle, first pointed out, so far as I am aware, by 
Humboldt in his memoir '' On Isothermal Lines and Distribu- 
tion of Heat over the Globe." t This principle may be stated 
as follows : — 

Although the total quantity of heat received by the earth 
from the sun in one revolution is inversely proportional to the 
minor axis of the orbit, yet this amoimt, as was proved 
by D'Alembert, is equally distributed between the two hemi- 
spheres, whatever the eccentricity may be. Whatever extra 
heat the southern hemisphere may at present receive from the 
sun daily during its summer months owing to greater proximity 
to the sun, is exactly compensated by a corresponding loss aris- 
ing from the shortness of the season ; and, on the other hand, 
whatever daily deficiency of heat we in the northern hemi* 
sphere may at present have during our summer half-year, in 
consequence of the earth's distance from the sun, is also exactly 
compensated by a corresponding length of season. 

But the surface temperature of our globe depends as muck 
upon the amount of heat radiated into space as upon the amount 
derived from the sun, and it has been thought by some that 
this compensating principle holds true only in regard to the 

• " Revolutions de la Mer," p. 37 (Beoond editioD). 
t Edin. Phil. Journ., toI. iv., p. 262 (1821). 



LOW TEMPERATURE OF S. HEMISPHERE. 8| 

latter. In the case of the Iieat lost by radiation the reverse is 
supposed to take place. The southern hemisphere, it is asserted, 
has not only a colder winter than the northern in consequence 
ol the son's greater distance, but it has also a longer winter ; 
and the extra loss of heat from radiation during winter is not 
compensated by its nearness to the sun during summer, for it 
gains no additional heat from this proximity. And in the 
same way it is argued that as our winter in the northern 
hemisphere, owing to the less distance of the sun, is not only 
warmer than that of the southern hemisphere, but is also at 
the same time shorter, so our hemisphere is not cooled to such 
an ^Ltent as the southern. And thus the mean temperature of 
the winter half-year, as well as the intensity of the sun's heat, 
is affected by a change in the sun's distance. 

Although I always regarded this cause of Humboldt's to be 
utterly inadequate to produce such effects as those attributed 
to it by Adh^mar, still, in my earlier papers * I stated it to be a 
vera causa which ought to produce some sensible effect on 
climate. But shortly afterwards on a more careful consideration 
of the whole subject, I was led to suspect that the circumstance 
in question can, i^MK)rding to theory, produce little or no effect 
on the climatic condition of our globe. 

As there appears to be a considerable amount of misappre- 
hension in reference to this point, which forms the basis of 
Adh^mar's theory, I may here give it a brief consideration.t 

The rate at which the earth radiates into space the heat 
xeceiyed from the sun depends upon the temperature of its 
surface ; and the temperature of its surface (other things being 
equal) depends upon the rate at which the heat is received. 
The greater the rate at which the earth receives heat from the 
sun, the greater will therefore be the rate at which it will lose 
that heat by radiation. Now the total quantity of heat re- 
seived during winter by the southern hemisphere is exactly 
» ♦ > 

• Phfl. Mng., { 4, vol. xxviii., p. 131. Jteader, December 2nd, 1865. 
t TliiB pomt wiU be found ducoased at considerable length in the FhiL Mag 
for September, 1S69. 



CLIMATE AND TIME. 

equal to that received during winter by the northern. But as 
the southern winter is longer than the northern, the rate at 
which the heat is received, and consequently the rate of radia- 
tion, during that season must be less on the southern hemi- 
sphere than on the northern. Thus the southern hemisphere 
loses heat during a longer period than the northern, and theie- 
fore the less rate of radiation (were it not for a circumstance 
presently to be noticed) would wholly compensate for the 
longer period, and the total quantity of heat lost during 
winter would be the same on both hemispheres. The southern 
sunmier is shorter than the northern, but the heat is more 
intense, and the surface of the ground kept at a higher tem- 
perature; consequently the rate of radiation into space is 
greater. 

When the rate at which a body receives heat is increased, 
the temperature of the body rises till the rate of radiation 
equals the rate of absorption, after which equilibrium is 
restored ; and when the rate of absorption is diminished, the 
temperature falls till the rate of radiation equals that of 
absorption. 

But notwithstanding all this, owing to the slow conductivity 
of the ground for heat, more heat will pass into it during the 
longer summer of aphelion than during the shorter one of 
perihelion; for the amount of heat which passes into the 
groimd depends on the length of time during which the earth 
is receiving heat, as well as upon the amount received. In 
like manner, more heat will pass out of the ground during the 
longer winter in aphelion than during the shorter one in 
perihelion. Suppose the length of the days on the one hemi- 
sphere (say the northern) to be 23 hours, and the length of 
the nights, say one hour ; while on the other hemisphere the 
days are one hour and the nights 23 hours. Suppose also that 
the quantity of heat received from the sun by the southern 
hemisphere during the day of one hour to be equal to that 
received by the northern hemisphere during the day of 23 
hours. It is evident that although the surface of the ground 



LOW TEMPERATURE OF S. HEMISPHERE. 85 

on the soutbem hemisphere would receive as much heat firom 
the sun during the short day of one hour as the surface of the 
northern hemisphere during the long day of 23 hours, yet, 
owing to the slow conductivity of the ground for heat, the 
amount absorbed woidd not be nearly so much on the southern 
hemisphere as on the northern. The temperature of the sur- 
face during the day, it is true, would be far higher on the 
southern hemisphere than on the northern, and consequently 
the rate at which the heat would pass into the ground would 
be greater on that hemisphere than on the northern ; but, 
notwithstanding the greater rate of absorption resulting from 
the high temperature of the surface, it would not compensate 
for the shortness of the day. On the other hand, the surface 
of the ground on the southern hemisphere would be colder 
during the long night of 23 hours thun it would be on the 
northern during the short night of only one hour; and the 
low temperature of the ground would tend to lessen the rate 
of radiation into space. But the decrease in the rate of radia- 
tion would not compensate fully for the great length of teh 
night. The general and combined result of all those causes 
would be that a slight accumulation of heat would take place 
on the northern hemisphere and a slight loss on the southern. 
But this loss of heat on the one hemisphere and gain on the 
other would not go on accumulating at a uniform rate year by 
year, as Adh^mar supposes. 

Of course we are at present simply considering the earth as 
an absorber and radiator of heat, without taking into account 
the effects of distribution of sea and land and other modifying 
causes, and are assuming that everything is the same in both 
hemispheres, with the exception that the winter of the one 
hemisphere is longer than that of the other. 

What, then, is the amoimt of heat stored up by the one 
hemisphere and lost by the other P Is it such an amount as 
to sensibly affect climate ? 

The experiments and observations which have been made on 
anderground temperature afford us a means of making at least 



86 CLIMATE AND TIME. 

a rough estimate of the amount. And from these it will be 
seen that the influence of an excess of seven or eight days in 
the length of the southern winter over the northern could 
hardly produce an effect that would be sensible. 

Observations were made at Edinburgh by Professor J. D. 
Forbes on three different substances; viz.^ sandstone^ sand, 
and trap-rock. Ey calculation, we find from the data afforded 
by those observations that the total quantity of heat accu- 
mulated in the ground during the summer above the mean 
temperature was as follows : — In the sandstone-rock, a quantity 
sufficient to raise the temperature of the rock 1^ C. to a depth 
of 85 feet 6 inches ; in the sand a quantity sufficient to raise 
the temperature 1° 0. to a depth of 72 feet 6 inches ; and in 
the trap-rock a quantity only sufficient to raise the temperature 
1° C. to a depth of 61 feet 6 inches. 

Taking the specific heat of the sandstone per unit volume^ as 
determined by Eegnault, at -4623, and that of sand at 'SOOe, 
and trap at '5283, and reducing all the results to one standard, 
viz., that of water, we find that the quantity of heat stored up 
in the sandstone would, if applied to water, raise its tempera- 
ture 1^ C. to a depth of 39 feet 6 inches ; that stored up in the 
sand would raise the temperature of the water 1^ C. to a depth 
of 21 feet 8 inches, and that stored up in the trap would raise 
the water 1° C. to the depth of 32 feet 6 inches. We may 
take the mean of these three results as representing pretty 
accurately the quantity stored up in the general surfece of the 
country. This would be equal to 31 feet 3 inches depth of 
water raised 1° 0. The quantity of heat lost by radiation 
during winter below the mean was found to be about equal to 
that stored up during summer. 

The total quantity of heat per square foot of surface received 
by the equator from sunrise till sunset at the time of the equi- 
noxes, allowing 22 per cent, for the amount cut off in passing 
through the atmosphere, is 1,780,474 foot-pounds. In the 
latitude of Edinburgh about 938,460 foot-pounds per square 
foot of surface is received, assuming that not more than 22 per 



LOW TEMPERATURE OF S. HEMISPHERE. 87 

cent. 18 cut o£E by the atmoepliere. At this rate a quantity of 
hieat would be receiyed from the sun in two days ten hours (say, 
three days) sufficient to raise the temperature of the water 1^ Gi 
to the required depth of 31 feet 3 inches. Consequently the 
total quantity of heat stored up during summer in the latitude 
of Edinburgh is only eqiial to what we receive from the sun 
during three days at the time of the equinoxes. Three days' 
sunshine during the middle of March or September, if appUed 
to raise the temperature of the groimd, would restore all the 
heat lost during the entire winter ; and another three days' 
sunshine would confer on the ground as much heat as is stored 
up during the entire summer. But it must be observed that 
the total duration of sunshine in winter is to that of summer 
in the latitude of Edinburgh only about as 4 to 7. Here is a 
difference of two months. But this is not all ; the quantity of 
heat received during winter is scarcely one-third of that received 
during summer ; yet, notwithstanding this enormous difference 
between summer and winter, the ground during winter loses 
only about six days' sun-heat below the maximum amount pes* 
sessed by it in summer. 

But if what has already been stated is correct, this loss of 
heat sustained by the earth during winter is not chiefly owing 
to radiation during the longer absence of the sun, but to the 
decrease in the quantity of heat received in consequence of 
his longer absence combined with the obliquity of his rays 
during that season. Now in the case of the two hemispheres, 
although the southern winter is longer than the northern, yet 
the quantity of heat received by each is the same. But suppos- 
ing it held true, which it does not, that the loss of heat sus- 
tained by the earth in winter is as much owing to radiation 
resulting from the excess in the length of the winter nights 
over those of the summer as to the deficiency of heat received 
in winter from that received in simmier, three days' heat would 
then in this case be the amount lost by radiation in consequence 
of this excess in the length of the winter nights. The total 
length of the winter nights to those of the summer is, as we 



g8 CLIMATE AND TIME. 

have seen, about as 7 to 4. This is a difference of nearly 1200 
hours. But the excess of the south polar winter over the 
north amounts to only about 184 hours. Now if 1200 hoars 
give a loss of three days' sun-heat, 184 hours will give a loss of 
scarcely 5^ hours. 

It is no doubt true that the two cases are not exactly analo 
gous ; but it is obvious that any error which can possibly arise 
from regarding them as such cannot materially alter the con- 
clusion to which we have arrived. Supposing the effect were 
double, or even quadruple, what we have concluded it to be, 
still it would not amount to a loss of two days' heat, which 
could certainly have little or no influence on climate. 

But even assuming all the preceding reasoning to be incor- 
rect, and that the southern hemisphere, in consequence of its 
longer winter, loses heat to the extravagant extent of 168 hours, 
supposed by Adh^mar, still this could not materially affect 
climate. The climate is influenced by the mere temperature of 
the surface of the ground, and not by the quantity of heat or 
cold that may be stored up under the surface. The climate is 
determined, so far as the ground is concerned, by the tempera- 
ture of the surface, and is wholly independent of the temperature 
which may exist imder the surface. Underground temperature 
can only affect climate through the surface. If the surface 
could, for example, be kept covered with perpetual snow, we 
should have a cold and sterile climate, although the tempera- 
ture of the ground imder the snow was actually at the boiling- 
point. Let the ground to a depth of, say 40 or 60 feet, be 
deprived of an amount of heat equal to that received from the 
sun in 168 hours. This could produce little or no sensible effect 
on climate ; for, owing to the slow conductivity of the ground 
for heat, this loss would not sensibly affect the temperature of 
the surface, as it would take several months for the sun's heat 
to penetrate to that depth and restore the lost heat. The cold, 
if I may be allowed to use the expression, would come so slowly 
out to the surface that its effect in lowering the temperature of 
the surface would scarcely be sensible. And, again, if we sup- 
pose the ] 68 hours' heat to be lost by the mere surface of tha 



LOW TEMPERATURE OF S. HEMISPHERE. 89 

ground, the effect would certainly be sensible, but it would only 
be 00 for a few days. We might in this case have a week's 
frozen soily but that would be all. Before the air had time to 
become yery sensibly affected by the low temperature of the 
surface the frozen soil would be thawed. 

The storing up of heat or cold in the groimd has in reality 
Tory little to do with climate. Some physicists explain, for 
example, why the month of July is warmer than June by refer- 
ring it to the fact that by the month of July the ground has 
become possessed of a larger accumulation of heat than it pos- 
sessed in June. This explanation is evidently erroneous. The 
ground in July certainly possesses a greater store of heat than 
it did in Jime; but this is not the reason why the former 
month is hotter than the latter. July is hotter than June 
because the air (not the ground) has become possessed of a 
larger store of heat than it had in June. Now the air Is 
warmer in July than in June because, receiving little increase 
of temperature from the direct rays of the sun, it is heated 
chiefly by radiation from the earth and by contact with its 
warm surface. Consequently, although the sun's heat is greater 
in June than it is in July, it is near the middle of July before 
the air becomes possessed of its maximum store of heat. We 
therefore say that July is hotter than June because the air is 
hotter, and consequently the temperature in the shade is greater 
in the former month than in the latter. 

It is therefore, I presume, quite apparent that Adh^mar's 
theory fSuls to explain why the southern hemisphere is colder 
than the northern. 

The generally/ accepted Explanation. — The difference in the 
mean temperature of the two hemispheres is usually attributed 
to the proportion of sea to land in the southern hemisphere 
and of land to sea in the northern hemisphere. This, no doubt, 
will account for the greater annual range of temperature on the 
northern hemisphere, but it seems to me that it will not account 
for the excess of mean temperature possessed by that hemisphere 
over the southern. 

The general influence of land on climate is to exaggerate the 



90 CLIMATE AND TIME. 

variation of temperature due to the seasons. On continents the 
summers are hotter and the winters colder than on the ocean. 
The days are also hotter and the nights colder on land than on 
sea. This is a result which follows from the mere physical pro- 
perties of land and water, independently of currents, whether of 
ocean or of air. But it nevertheless follows, according to theory 
(and this is a point which has been overlooked), that the mean 
annual temperature of the ocean ought to be greater than that 
of the land in equatorial regions as well as in temperate and 
polar regions. This will appear obvious for the following 
reasons: — (1) The ground stores up heat only by the slow 
process of conduction, whereas water, by the mobility of its 
particles and its transparency for heat-rays, especially those 
&om the sun, becomes heated to a considerable depth rapidly. 
The quantity of heat stored up in the ground is thus compara- 
tively small, while the quantity stored up in the ocean is great. 
(2) The air is probably heated more rapidly by contact with 
the ground than with the ocean ; but, on the other hand, it is 
heated fiir more rapidly by radiation from the ocean than from 
the land. The aqueous vapour of the air is to a great extent 
diathermanous to radiation from the ground, while it absorbs 
the rays from water and thus becomes heated. (3) The air 
radiate back a considerable portion of its heat, and the ocean 
absorbs this radiation from the air more readily than the 
ground does. The ocean will not reflect the heat from the 
aqueous vapour of the air, but absorbs it, while the ground 
does the opposite. Eadiation &om the air, therefore, tends 
more readily to heat the ocean than it does the land. (4) The 
aqueous vapour of the air acts as a screen to prevent the loss by 
radiation from water, while it allows radiation from the ground 
to pass more freely into space ; the atmosphere over the ocean 
consequently throws back a greater amount of heat than is 
thrown back by the atmosphere over the land. The sea in this 
ease has a much greater difficulty than the land has in getting 
quit of the heat received from the sun ; in other words, the 
land tends to lose its heat more rapidly than the sea. The 



LOW TEMPERATURE OF S. HEMISPHERE. 91 

oonaequenoe of all these circuinstances is that the ocean must 
•tand at a higher mean temperature than the land. A state of 
equilibrium is noTer gained until the rate at which a body is 
receiving heat is equal to the rate at which it is losing it ; but 
as equal surfisuies of sea and land receive from the sun the same 
amount of heat, it therefore follows that, in order that the sea 
may get quit of its heat as rapidly as the land, it mu^t stand at 
a higher temperature than the land. The temperature of the sea 
must continue to rise till the amount of heat thrown off into 
qpace equals that received from the sim ; when this point is 
reached, equilibrium is established and the temperature remains 
stationary. But, owing to the greater difficulty that the sea 
has in getting rid of its heat, the mean temperature of equili- 
brium of the ocean must be higher than that of the land ; con- 
sequently the mean temperature of the ocean, and also of the 
air immediately over it, in tropical regions should be higher 
than the mean temperature of the land and the air over it. 

The greater portion of the southern hemisphere, however, is 
occupied by water, and why then, it may be asked, is this water 
hemisphere colder than the land hemisphere ? Ought it uot also 
to follow that the sea in inter-tropical regions should be warmer 
than the land under the same parallels ; yet, as we know, the 
reverse is actually found to be the cose. How then is all this 
to be explained, if the foregoing reasoning be correct P We 
find when we examine Professor Dove's charts of mean annual 
temperature, that the ocean m inter- tropical regions has a mean 
annual temperature below the normal, and the land a mean 
annual temperature above the normoL Both in the Pacific 
and in the Atlantic the mean temperature sinks to 2^*3 below 
the normal, while on the land it rises 4^*6 above the normal. 
The explanation in .this case is obviously this : the temperature 
of the ocean in inter-tropical regions, as we have already 
seen, is kept much lower than it would otherwise be by 
the enormous amount of Jieai that is being constantly carried 
away from those regions into temperate and polar regions, and 
of cold that is being constantly carried from temperate and 



$s CLIMATE AND TIME. 

polar regions to the tropical regions by means of ocean- 
currents. The same principle whiuh explains why the sea in 
inter-tropical r^ons has a lower mean annual temperature 
than the land, expkins also why the southern hemisphere has 
a lower mean annual temperature than the northern. The 
temperature of the southern hemisphere is lowered by the 
transference of heat by means of ocean-currents. 

Heat tramferred from the Southern to the Norfltcrn Jletni- 
tphere hy Ocmn-currenfa the true Explanation. — The great ocoan- 
currcnta of the globe take their rise in three immense streams 
from the Southern Ocean, which, on reaching the tropical 
regions, become deflected in a westerly direction and flow 
along the southern side of the equator for thousands of miles. 
Perhaps more than one half of this mass of moving water 
returns into tho Southern Occnn without ever crossing the 
equator, but tho quantity which crosses over to the northern 
hemisphere is enormous. This constant flow of water from the 
southern hemisphere to tho northern in the form of surface 
currents must be com^iensatcd by under currents of equal magni- 
tude from the northern hemisphere to the southern. The 
currents, however, which cross the equator are far higher 
in temperature than their compensating under currents ; conse- 
quently there is a constant transference of heat from the 
southern hemisphere to tho northern. Any currents taking 
their rise in tho northern hemisphere and flowing across into 
the southern are comparatively trifling, and the amount of 
heat transferred by them is also trifling. There are one or 
two corrents of considerable size, suob as the Brazilian branch 
of the great equatorial current of the Atlantic, and a part of 
the South Eqaatoriol Dzift-corrent of the Pacific, which cross 
the eqiutoT frna nortii to Mnth ; bat these cannot be regarded 
us northern currents; they are simply Bonthem currents 
defleotod back after crossing over to the northern hemisphere. 
Tho hcjit which thono currents poesoGs is chiefly obtained on 
cJumispbere before crossing over to the northern ; 
I hemisphere may not gain much 



LOW TEMPERATURE OF S. HEMISPHERE. 93 

lieat by means of them, it, on the other hand, does not lose 
much, for the heat which they give out in their progress along 
the southern hemisphere does not belong to the northern 
hemisphere. 

But, after making the fullest allowance for the amoimt of 
heat carried across the equator from the northern hemisphere 
to the southern, we shall find, if we compare the mean tem- 
perature of the currents from south to north with that of 
the great compensating under currents and the one or two 
small surface currents, that the former is very much higher 
than the latter. The mean temperature of the water crossing 
the equator from south to north is probably not under 65°, 
that of the imder currents is probably not over 39°. But to 
the under currents we must add the surface currents from 
north to south ; and assuming that this will raise the mean 
temperature of the entire mass of water flowing south to, say, 
45°, we have still a diflference of 20° between the temperature 
of the masses flowing north and south. Each cubic foot of 
water which crosses the equator will in this case transfer about 
965,000 foot-potmds of heat from the southern hemisphere to 
the northern. If we had any moans of ascertaining the 
volume of those great currents crossing the equator, we should 
then be able to make a rough estimate of the total amount of 
heat transferred from the southern hemisphere to the northern ; 
but as yet no accurate estimate has been made on this point. 
Let US assume, what is probably below the truth, that the 
total amount of water crossing the equator is at least double 
that of the Gulf-stream as it passes through the Straits of 
Florida, which amount we have already found to be equal to 
66,908,160,000,000 cubic feet daily. Taking the quantity of 
heat conveyed by each cubic foot of water of the Gulf-stream 
as 1,158,000 foot-pounds, it is found, as we have seen, that an 
amount of heat is conveyed by this current equal to all the heat 
that falls within 32 miles on each side of the equator. Then, 
if each cubic foot of water crossing the equator transfers 
966«000 foot-pounds, and the quantity of water be double that 



94 CLIMATE AND TIME. 

of the Gxilf-Btream, it follows that the amoxmt of heat trans- 
ferred from the southern hemisphere to the northern is equal 
to all the heat falling within 62 miles on each side of the 
equator^ or equal to all the heat falling on the southern hemi^ 
sphere within 104 miles of the equator. This quantity taken 
from the southern hemisphere and added to the northern wOl 
therefore make a difference in the amoimt of heat possessed by 
the two hemispheres equal to all the heat which Mis oH the 
southern hemisphere within somewhat more than 208 miles of 
the equator. 

A large Portion of the Heat of the Oulf-stream derived from 
the Southern Hemisphere. — It can be proved that a very large 
portion of the heat conveyed by the Gfulf-stream comes ttom 
the southern hemisphere. The proof is as follows : — 

If all the heat came from the northern hemisphere, it could 
only come from that portion of the Atlantic, Caribbean Sea, 
and Gulf of Mexico which lies to the north of the equator. 
The entire area of these seas, extending to the Tropio of 
Cancer, is about 7,700,000 square miles. But this area is not 
sufficient to supply the current passing through the " Narrows " 
with the necessary heat. Were the heat which passes through 
the Straits of Florida derived exclusively from this area, the 
following table would then represent the relative quantity per 
unit surface possessed by the Atlantic in the three zones, 
assiuning that one half of the heat of the Gulf- stream passes 
into the arctic regions and the other half remains to warm the 
temperate regions* :— 

From the equator to the Tropic of Canrer . . . 778 
From the Tropic of Cancer to the Arctic Circle . S48 

From the Arctic Circle to the North Pole . . . 610 

These figures show that the Atlantic, from the equator to the 
Tropic of Cancer, would be as cold as from the Tropic of Cancer 
to the North Pole, were it not that a large proportion of the 
heat possessed by the Gidf-stream is derived from the southern 
hemisphere. 

• See Phil. Mag. for October, 1870, p. 269. 



CHAPTER VI. 

BXAIONATION OF THE GRAVITATION THEORY OF OCEANIC CIRCULA* 

TION. — LIEUT. MAURT's THEORY. 

Inirodaciion. — Ocean-currents, according to Maury, dae to Difference of Speciflo 
OraTitj. — Difference of Specific Qravity resulting from Difference of Tem- 
pezatore. — Difference of Specific Gravity resulting from Difference of Sult- 
neas. — Maury's two Causes neutralize each other. — Uow, according to him, 
Difference in Saltness acts as a Cause. 

Introduction. — Few subjects have excited more interest and 
attention than the cause of ocean circulation ; and yet few are 
in a more imperfect and unsatisfactory condition, nor is there 
any question regarding which a greater diversity of opinion 
has prevailed. Our incomplete acquaintance with the facts 
relating to the currents of the ocean and the modes of circula- 
tion actually in operation, is no doubt one reason for this state 
of things. But doubtless the principal cause of such diversity 
of opinion lies in the fact that the question is one which 
properly belongs to the domain of physics and mechanics, 
while as yet no physicist of note (if we except Dr. Colding, of 
Copenhagen) has given, as far as I know, any special attention 
to the subject. It is true that in works of meteorology and 
physical geography reference is continually made to such 
eminent physicists as Herschel, Pouillet, Buff, and others ; 
but when we turn to the writings of these authors we find 
merely a few remarks expressive of their opinions on the 
subject, and no special discussion or investigation of the 
matter, nor anything which could warrant us in concluding 
that such investigations have ever been made. At present the 
question cannot be decided by a reference to authorities. 



96 CLIMATE AND TIME. 

The yarious theories on the subject may be classed under 
two divisions ; the first of these attributes the motion of the 
water to the impuhe of the tcind, and the second to the force of 
gravity resulting from difference of density. But even amongst 
those who adopt the former theory, it is generally held that 
the winds are not the sole cause, but that, to a certain extent 
at least, difierence of specific gravity contributes to produce 
motion of the waters. This is a very natural conclusion ; and 
in the present state of physical geography on this subject one 
can hardly be expected to hold any other view. 

The supporters of the latter theory may be subdivided into 
two classes. The first of these (of which Maury may be re- 
garded as the representative) attributes the Gidf-stream, and 
other sensible currents of the ocean, to diiference of specific 
gravity. The other class (at present the more popular of the 
two, and of which Dr. Carpenter may be considered the repre- 
sentative) denies altogether that such currents can be produced 
by difference of specific gravity,* and affirms that there is a 
general movement of the upper portion of the ocean from the 
equator to the poles, and a counter-movement of the under 
portion from the poles to the equator. This movement is attri- 
buted to difference of specific gravity between equatorial and 
polar water, resxdting from difference of temperature. 

The widespread popxdarity of the gravitation theory is no 
doubt, to a great extent, owing to the very great prominence 
given to it by Lieut. Maury in his interesting and popular 
work, " The Physical Geography of the Sea." Another cause 
which must have favoured the reception of this theory is the 
ease with which it is perceived how, according to it, circulation 
of the waters of the ocean is supposed to follow. One has no 
difficulty, for example, in perceiving that if the inter- tropical 
waters of the ocean are expanded by heat, and the waters 
around the poles contracted by cold, the surface of the ocean 
will stand at a higher level at the equator than at the poles. 
Equilibrium being thus disturbed, the water at the equator 
* Proceedings of the Boyal Society, No. 13S, p. 696, foot-note. 



THE GRA VITATION THEORY. 97 

will tend to flow towards the poles as a surface current, and 
the water at the poles towards the equator as an under current. 
Thisy at first sight, looks well, especially to those who take 
but a superficial view of the matter. 

We shall examine this theory at some length, for two 
reasons : 1, because it lies at the root of a great deal of the 
confusion and misconception which have prevailed in regard to 
the whole subject of ocean-currents : 2, because, if the theory 
is correct, it militates strongly against the physical theory of 
secular changes of climate advanced in this volume. We 
have already seen (Chapter IV.) that when the eccentricity 
of the earth's orbit reaches a high value, a combination of 
physical circumstances tends to lower the temperature of the 
hemisphere which has its winter solstice in aphelion, and to 
raise the temperature of the opposite hemisphere, whose winter 
solstice will, of course, be in perihelion. The direct result of 
this state of things, as was shown, is to strengthen the force of 
the trade-winds on the cold hemisphere, and to weaken their 
strength on the warm hemisphere : and this, in turn, we also 
saw, tends to impel the warm water of the inter-tropical region 
on to the warm hemisphere, and to prevent it, in a very large 
degree, from passing into the cold hemisphere. This deflection 
of the ocean-currents tends to an enormous extent to increase 
the diflerence of temperature previously existing between the 
two hemispheres. In other words, the warm and equable con- 
dition of the one hemisphere, and the cold and glacial condition 
of the other, are, to a great extent, due to this deflection of 
ocean-currents. But if the theory be correct which attributes 
the motion of ocean-currents to a difierence in density between 
the sea in inter- tropical and polar regions, then it follows that 
these currents (other things being equal) ought to be stronger 
on the cold hemisphere than on the warm, because there is a 
greater diflerence of temperature and, consequently, a greater 
diflerence of density, between the polar seas of the cold hemi- 
sphere and the equatorial seas, than between the polar seas of 
the warm hemisphere and the equatorial seas. And this being 



q8 CLIMATE AND TIME. 

the case^ notwitliBtanding the influence of the trade^ winds of 
the cold hemisphere blowing over upon the warm, the currents 
willy in all probability, be stronger on the cold hemisphere than 
on the warm. In other words, the influence of the powerful 
trade-winds of the cold hemisphere to transfer the warm water 
of the equator to the warm hemisphere will probably be 
more than counterbalanced by the tendency of the warm and 
buoyant waters of the equator to flow towards the dense and 
oold waters around the pole of the cold hemisphere. But if 
ooean-currents are due not to difierence in specific gravilyy bat 
to the influence of the winds, then it is evident that the waters 
at the equator will be impelled, not into the cold hemisphen^ 
but into the warm. 

For this reason I have been the more anxious to proye. that 
inter-tropical heat is conveyed to temperate and polar regions 
by ocean-currents, and not by means of any general movement 
of the ocean resulting from difference of gravity. I shall 
therefore on this account enter more fully into this part of the 
subject than I otherwise would have done. Irrespective of all 
this, however, the important nature of the whole question, and 
the very general interest it excites, warrant a full consideration 
of the subject. 

I shall consider first that form of the gravitation theory 
advocated by Maury in his work on the " Physical Creography 
of the Sea,'' which attributes the motion of the GuK-stream and 
other sensible currents of the ocean to differences of specific 
gravity. One reason which has induced me to select Maury's 
work is, that it not only contains a much filler discussion on 
the cause of the motion of ocean-currents than is to be found 
anywhere else, but also that it has probably passed through a 
greater number of editions than any other book of a scientific 
character in the English language in the same length of time. 

Examination of Lieut Mauris Oravttation Theory. — ^Although 
Lieut. Maury has expounded his views on the cause of ocean- 
currents at great length in the various editions of his work, yet 
it is somewhat difficult to discover what they really are. This 



THE GRA VITA TION THEORY. 99 

arises chiefly firom the generallj confused and sometimes con* 
tradictory nature of his hydrodynamical conceptions. After a 
repeated perusal of seyeral editions of his book, the following, I 
trOBt, will be found to be a pretty accurate representation of his 
theory: — 

(hean^currenUy according to Maury, due to Difference of Specific 
Gravity. — Although Maury alludes to a number of causes whichi 
he thinks, tend to produce currents, yet he deems their in- 
fluence so snuill that, practically, all currents may be referred 
to difference of specific gravity. 

'' K we except," he says, '' the tides, and the partial currents 
of the sea, such as those that may be created by the wind, we 
may lay it down as a rule that all the currents of the ocean 
owe their origin to the differences of specific gravity between 
sea-water at one place and sea-water at another ; for wherever 
there is such a difference, whether it be owing to difference of 
temperature or to difference of saltness, &c., it is a difference 
that disturbs equilibrium, and currents are the consequence ** 
(S 467) ♦. To the same effect see §§ 896, 37, 612, 620, and 637. 

Notwithstanding the fact that he is continually referring to 
difference of specific gravity as the great cause of currents, it is 
difficult to understand in what way he conceives this difference 
to act as a cause. 

Difference of specific gravity between the waters of the ocean 
at one place and another can give rise to currents only through 
the influence of the earth's gravity. All currents resulting 
from difference of specific gravity can be ultimately resolved 
into the general principle that the molecules that are specific- 
ally heavier descend and displace those that are specifically 
lighter. If, for example, the ocean at the equator be expanded 
by heat or by any other cause, it will be forced by the denser 
waters in temperate and polar regions to rise so that its surface 
shall stand at a higher level than the surface of the ocean in 

* The edition from which I qnote, unless the contraiy is stated, is the one 
puhliahed hy Messrs. T. Nelson and Sons, 1870, which is a reprint of the new 
edition puhlished in 1859 hy Messrs. Siimpson Low and Co. 



loo CLIMATE AND TIME. 

lliese regions. The surface of the ocean will become an in* 
clined plane, sloping from the equator to the poles. Hydro- 
statically, the ocean, considered as a mass, will then be in a 
state of equilibriimi ; but the individual molecules will not 
be in equilibrium. The molecules at the sur&ce in this case 
may be regarded as lying on an inclined plane sloping from the 
equator down to the poles, and as these molecules are at liberty 
to move they will not remain at rest, but will descend the 
incline towards the poles. When the waters at the equator are 
expanded, or the waters at the poles contracted, gravitation 
makes, as it were, a twofold effort to restore equilibrium. It 
in the first place sinks the waters at the poles, and raises the 
waters at the equator, in order that the two masses may balance 
each other ; but this very effort of gravitation to restore equi- 
librium to the mass destroys the equilibrium of the molecules 
by disturbing the level of the ocean. It then, in the second 
place^ endeavours to restore equilibrium to the molecules by 
pulling the lighter surface water at the equator down the 
incline towards the poles. This tends not only to restore the 
level of the ocean, but to bring the lighter water to occupy the 
surface and the denser water the bottom of the ocean ; and 
when this is done, complete equilibrium is restored, both to the 
mass of the ocean and to its individual molecules, and all 
further motion ceases. But if heat be constantly applied to 
the waters of the equatorial regions, and cold to those of the 
polar regions, and a permanent disturbance of equilibrium 
maintained, then the continual effort of gravitation to restore 
equilibrium will give rise to a constant current. In this case, 
the heat and the cold (the agents which disturb the equilibrium 
of the ocean) may be regarded as causes of the current, inas- 
much as without them the current would not exist; but the 
real eflScient cause, that which impels the water forward, is the 
force of gravity. But the force of gravity, as has already been 
noticed, cannot produce motion (perform work) unless the thing 
acted upon descend. Descent is implied in the very conception 
of a current produced by difference of specific gravity. 



THE GRAVITATION THE&Ry. loi 



•./i 



But Maury speaks as if difference of specjiA^ gravity could 
give rise to a current without any descent. . ' • 

**It is not necessary," he says, "to associate .with oceanic 
currents the idea that they must of necessity, asTo^'land, run 
firom a higher to a lower level. So far from this Being the 
case, some currents of the sea actually run up hill, while others 
run on a level. The Gulf-stream is of the first class ** (§-403). 
" The top of the Gulf-stream runs on a level with the'c^^eUji ; 
therefore we know it is not a descending current " (§*1^). 
And in § 9 he says that between the Straits of Florida ar^d' 
Cape Hatteras the waters of the Ghilf-stream "are actuatfjr^; 
forced up an inclined plane, whose submarine ascent is 
not less than 10 inches to the mile." To the same effect see ' 
IS 25, 69. 

It is perfectly true that " it is not necessary to associate with 
ocean-currents the idea that they must of necessity, as on land, 
run from a higher to a lower level." But the reason of this is 
that ocean-currents do not, like the currents on land, owe their 
motion to the force of gravitation. If ocean-currents result 
from difference of specific gravity between the waters in tropical 
and polar regions, as Maury maintains, then it is necessary to 
assume that they are descending currents. Whatever be the 
cause which may give rise to a difference of specific gravity, the 
motion which results from this difference is due wholly to the 
force of gravity ; but gravity can produce no motion unless 
the water descend. 

This fact must be particularly borne in mind while we are 
considering Maury's theory that currents are the result of 
difference of specific gravity. 

Ocean-currents, then, according to that writer, owe their 
existence to the difference of specific gravity between the waters 
of inter-tropical and polar regions. This difference of specific 
gravity he attributes to two causes — (1) to difference as to tem- 
perature ^ (2) to difference as to saltness. There are one or two 
causes of a minor nature affecting the specific gravity of the 
sea, to whicli he alhides ; but these two determine the general 









loa . eJLIMATE AND TIME. 

•• . • 
result. Let u^-ldegfm with the consideration of the first of these 
two causes, vi5r..j — 

Differeiio^*of^ Specific Oravity resulting from Difference of Tem^ 
perature»-^^*ii[B.UTj explains his views on this point by means oi 
an illustratrdn. *' Let us now suppose/' he says, '* that all the 
water Witliin the tropics, to the depth of one hundred jGathomB, 
sudd^&lybecomes oil. The aqueous equilibrium of the planet 
waijitdL'«thereby be disturbed, and a general system of currents 
ajld%*Counter currents would be immediately commenced — ^tlia 
Vttl^in an unbroken sheet on the surface, running toward the 
r.'.^les, and the water, in an under current^ toward the equator^ 
*'. The oil is supposed, as it reaches the polar basin, to be recon- 
verted into water, and the water to become oil as it orossea 
Cancer and Capricorn, rising to the surface in inter-tropical 
regions, and returning as before " (§ 20). " Now," he says 
(§ 22), " do not the cold waters of the north, and the warm 
waters of the Gulf, made specifically lighter by tropical heat, 
and which we see actually preserving such a system of counter- 
currents, hold, at least in some degree, the relation of the 
supposed water and oil P " 

In § 24 he calculates that at the Narrows of Bemini the 
difference in weight between the volume of the Gulf-water 
that crosses a section of the stream in one second, and an equal 
volume of water at the ocean temperature of the latitude, sup- 
posing the two volumes to be equally salt, is fifteen millions of 
pounds. Consequently the force per second operating to propel 
the waters of the Gulf towards the pole would in this case, he 
concludes, be the ** equilibrating tendency due to fifteen millions 
of pounds of water in the latitude of Bemini." In §§ 511 and 
512 he states that the effect of expanding the waters at the 
torrid zone by heat, and of contracting the waters at the 
frigid zone by cold, is to produce a set of surface-currents of 
warm and light water from the equator towards the poles, and 
another set of under currents of cooler and heavy water from 
the poles towards the equator. (See also to the same effect 
§§ 613, 514, 896.) 



THE GRAVITATION THEORY. 103 

There con be no doubt tbat his conclusion is that the watei*s 
in inter-tropical regions are expanded by heat, while those in 
polar regions are contracted by cold, and that this tends to 
produce a surface current from the equator to the poles, and an 
under current from the poles to the equator. 

We shall now consider his second great cause of ocean- 
currents, viz. : — 

Difference of Specific Oratity resulting from Difference in Degree 
of ScUtfiess, — Maury maintains, and that correctly, that saltness 
increases the density of water — that, other things being equal, 
the saltest water is the densest. He suggests '* that one of the 
purposes which, in the grand desigpi, it was probably intended 
to accomplish by having the sea salt and not fresh, was to 
impart to its waters the forces and powers necessary to make 
their circulation complete" (§ 495). 

Now it is perfectly obvious that if difference in saltness is to 
co-operate with difference in temperature in the production of 
ocean-currents, the saltest waters, and consequently the densest, 
must be in the polar regions, and the waters least salt, and 
consequently lightest, must be in equatorial and inter-tropical 
regions. Were the saltest waters at the equator, and the 
freshest at the poles, it would tend to neutralize the effect due 
to heat, and, instead of producing a current, would simply tend 
to prevent the existence of the currents which otherwise would 
result from difference of temperature. 

A very considerable portion of his work, however, is devoted 
to proving that the waters of equatorial and inter-tropical 
regions are Salter and heavier than those of the polar regions ; 
and yet, notwithstanding this, he endeavours to show that this 
difference in respect to saltness between the waters of the 
equatorial and the polar regions is one of the chief causes, if 
not the chief cause, of ocean-currents. In fact, it is for this 
special end that so much labour is bestowed in proving that the 
saltest water is in the equatorial and inter-tropical regions, and 
the freshest in the polar. 

"In the present state of our knowledge," he says, "con* 
6 



104 CLIMATE AND TIME. 

ceming this wonderful pbenomenon (for the Gulf -stream is one 
of the most marvellous things in the ocean) we can do little 
more than conjecture. But we have two causes in operation 
which we may safely assume are among those concerned in 
producing the Gulf-stream. One of these is the increased salt- 
ness of its water after the trade- winds have been supplied with 
vapour from it, be it much or little; and the other is the 
diminished quantum of salt which the Baltic and the Northern 
Seas contain " (§ 37). " Now here we have, on one side, the 
Caribbean Sea and Gulf of Mexico, with their waters of 
brine ; on the other, the great Polar Basin, the Baltic, and the 
North Sea, the two latter with waters that are but little more 
than brackish. In one set of these sea-basins the water is heavy, 
in the other it is light. Between them the ocean intervenes ; 
but water is bound to seek and to maintain its level ; and here, 
therefore, we unmask one of the agents concerned in causing 
the Gulf-stream" (§ 38). To the same effect see §§ 52. 522, 
523, 524, 525, 526, 528, 530, 554, 556. 

Lieut. Maury's two cau%e% neutralize each other. Here we 
have two theories put forth regarding the cause of ocean- 
currents, the one in direct opposition to the other. According 
to the one theory, ocean-currents exist because the waters of 
equatorial regions, in consequence of their higher temperature, 
are leas dense than the waters of the polar regions ; but according 
to the other theory, ocean-currents exist because the waters of 
equatorial regions, in consequence of their greater saltness, are 
more dense than the waters of the polar regions. If the one 
cause be assigned as a reason why ocean-currents exist, then 
the other can be equally assigned as a reason why they should not 
exist. According to both theories it is the difference of density 
between the equatorial and polar waters that gives rise to cur- 
rents ; but while the one theory maintains that the equatorial 
waters are lighter than the polar, the other holds that they are 
heavier. Either the one theory or the other may be true, or 
neither ; but it is logically impossible that both of them can. 
Let it be observed that it is not two currents, the one contrary 



THE GRAVITATION THEORY. 10$ 

to the other, with which we have at present to do ; it is not 
temperature producing currents in one direction^ and saltness 
producing currents in the contrary direction. We have two 
theories regarding the origin of currents^ the one diametrically 
opposed to the other. The tendency of the one cause assigned 
is to prevent the action of the other. If temperature is allowed 
to act, it will make the inter-tropical waters lighter than the 
polar, and then, according to theory, a current will result. But 
if we bring saltness into play (the other cause) it will do the 
reverse : it will increase the density of the inter-tropical waters 
and diminish the density of the polar ; and so far as it acts it 
will diminish the currents produced by temperature, because it 
will diminish the difference of spocitic gravity between the 
inter-tropical and polar regions which had been previously 
caused by temperature. And when the effects of saltness are as 
powerful as those of temperature, the difference of specific 
gravity produced by temperature will be completely effaced, or, 
in other words, the waters of the equatorial and polar seas will 
be of the same density, and consequently no current will exist. 
And so long as the two causes continue in action, no current 
can arise, imless the energy of the one cause should happen to 
exceed that of the other ; and even then a current will only 
exist to the extent by which the strength of the one exceeds 
that of the other. 

The contrary nature of the two theories will be better seen 
by considering the way in which it is supposed that difference 
in saltness is produced and acts as a cause. 

If there is a constant current resulting from the difference in 
saltness between the equatorial and polar waters, then there 
must be a cause which maintains this difference. The current 
is simply the effort to restore the equilit)rium lost by the 
difference ; and the current would very soon do this, and then 
all motion would cease, were there not a constantly operating 
cause maintaining the disturbance. What, then, according to 
Maury, is the cause of this disturbance, or, in other words, 
what is it that keeps the equatorial waters Salter than the polar P 



io6 CLIMATE AND TIME. 

The dgencies in operation are stated by him to be heati 
radiation, evaporation, precipitation, and secretion of solid 
matter in the form of shells, &c. The two most important, 
however, are evaporation and precipitation. 

The trade-winds enter the equatorial regions as relatively 
dry winds thirsting for vapour ; consequently they absorb far 
more moisture than they give out ; and the result is that 
in inter-tropical regions, evaporation is much in excess of 
precipitation ; and as fresh water only is taken up, the salt 
being left behind, the process, of course, tends to increase the 
saltness of the inter-tropical seas. Again, in polar and extra- 
tropical regions the reverse is the cose; precipitation is in 
excess of evaporation. This tends in turn to diminish the 
saltness of the waters of those regions. (See on these poin' ^ 
S§ 31, 33, 34, 37, 179, 517, 526, and 652.) 

In the system of circulation produced by difference of tem- 
perature, us we have already seen, the surface-current* flow 
from tlie equator to the poles, and the under or return currents 
from the poles to the equator ; but in the system produced by 
difference of saltness, the surface currents flow from the poles 
to the equator, and the return under currents from the equator 
to the poles. That the surface currents produced by difference 
of saltness flow from the poles to the equator, Maury thinks is 
evident for the two following reasons : — 

(1) As evaporation is in excess of precipitation in inter- 
tropical regions, more water is taken off the surface of the ocean 
in those regions than falls upon it in the form of rain. This 
excess of water falls in the form of rain on temperate and 
polar regions, where, consequently, precipitation is in excess 
of eNnporation. The lifting of the water off the equatorial 
regions and its deposit on the polar tend to lower the level of 
the ocean in equatorial regions and to raise the level in polar ; 
consequently, in order to restore the level of the ocean, the 
surface water at the polar regions flows towards the equatorial 
r^ons. 

01) At the water taken up at the equator is fresh, and thi 



THE GRAVITATION THEORY. 107 

nit iB left belundy the ocean^ in inter-tropical regions, is thus 
made Salter and consequently denser. This dense water, there- 
fore, sinks and passes away as an under current. This water, 
evaporated from inter-tropical regions, falls as fresh and lighter 
water in temperate and polar regions ; and therefore not only 
is the level of the ocean niised, but the waters are made lighter. 
Hence, in order to restore equilibrium, the waters in temperate 
and polar regions will flow as a surface current towards the 
equator. Under currents will flow from the equator to the poles, 
and surface or upper currents from the poles to the equator. 
Difference in temperature and difference in saltness, therefore, 
in every respect tend to produce opposite effects. 

That the above is a fair representation of the way in which 
Mauiy supposes difference in saltness to act as a cause in the 
production of ocean-currents will appear from the following 
quotations : — 

'' In those regions, as in the trade-wind region, where evapo- 
ration is in excess of precipitation, the general level of this 
supposed sea would be altered, and immediately as much water 
as is carried off by evaporation would commence to flow in 
from north and south toward the trade-wind or evaporation 
region, to restore the level " (§ 509). " On the other hand, the 
winds have taken this vapour, borne it off to the extra-tropical 
regions, and precipitated it, we will suppose, where precipitation 
is in excess of evaporation. Here is another alteration of sea- 
level, by elevation instead of by depression ; and hence we 
have the motive power for a surface current from each pole 
towards the equator, the object of which is only to supply the 
demand for evaporation in the trade- wind regions " (§ 510). 

The above result would follow, supposing the ocean to be 
fresh. He then proceeds to consider an additional result that 
follows in consequence of the saltness of the ocean. 

*' Let evaporation now commence in the trade- wiud region, 
as it was supposed to do in the case of the fresh- water seas, 
and as it actually goes on in nature — and what takes place P 
Why a lowering of the sea-level as before. But as the \apoiir 



io8 CLIMATE AND TIME. 

of salt water is fresh, or nearly so, fresh water only is taken np 
from the ocean ; that which remains behind is therefore more 
salt. Thus, while the level is lowered in the salt sea^ the 
equilibrium is destroyed because of the saltness of the water ; 
for the water that remains after evaporation takes place is, on 
account of the solid matter held in solution, specifically heavier 
than it was before any portion of it was converted into vapour '* 
(§ 517). 

" The vapour is taken from the surface-water ; the surface- 
water thereby becomes more salt, and, under certain conditions, 
heavier. When it becomes heavier, it sinks; and hence we 
have, due to the salts of the sea, a vertical circulation, namely, 
a descent of heavier — because salter and cooler — ^water from 
the surface, and an ascent of water that is lighter — ^because it 
is not so salt — ^from the depths below " (§ 518). 

In section 519 he goes on to show that this vapour removed 
from the inter-tropical region is precipitated in the polar 
regions, where precipitation is in excess of evaporation. " In 
the precipitating regions, therefore, the level \s destroyed, as 
before explained, by elevation, and in the evaporating regions 
by depression ; which, as already stated, gives rise to a system 
of surface currents, moved by gravity alone, from the poles 
totoards the equator " (§ 520). 

"This fresh water being emptied into the Polar Sea and 
agitated by the winds, becomes mixed with the salt; but as 
the agitation of the sea by the winds is supposed to extend to 
no great depth, it is only the upper layer of salt water, and that 
to a moderate depth, which becomes mixed with the fresh. The 
specific gravity of this upper layer, therefore, is diminished 
just as much as the specific gravity of the sea-water in the 
evaporating regions was increased. And thus we have a surface 
current of saltish water from the poles towards the equator, and 
an under current of water salter and heavier from the equator to 
the poles'' (§522). 

"This property of saltness imparts to the waters of the 
ocean another peculiarity, by which the sea is still better 



THE GRAVITATION THEORY. 109 

adapted for tlie regulation of climates, and it is this : by evapo- 
rating fresli water from the salt in the tropics, the surface 
water becomes heavier than the average of sea- water. This 
heavy water is also warm water ; it sinks, and being a good 
retainer, but a bad conductor, of heat, this water is employed 
in transporting through under currents heat for the mitigation 
of climates in far distant regions'' (§ 526). 

** For instance, let ns suppose the waters in a certain part 
of the torrid zone to be 90^, but by reason of the fresh water 
which has been taken from them in a state of vapour, and con- 
sequently, by reason of the proportionate increase of salts, 
these waters are heavier than waters that may be cooler, but 
not so salt. This being the case, the tendency would be for 
this warm but salt and heavy water to flow off as an under 
current towards the polar or sotne other regiom of lighter water ** 
(§ 554). 

That Maury supposes the warm water at the equator to flow 
to the polar regions as an under current is further evident from 
the &ct that he maintains that the climate of the arctic regions 
is mitigated by a warm under current, which comes from the 
equatorial regions, and passes up through Davis Straits (see 
S$ 534— 644). 

The question now suggests itself: to which of these two 
antagonistic, causes does Maury really suppose ocean-currents 
must be referred? Whether does he suppose, difierence in 
temperature or diflerence in saltness, to be the real cause P I 
have been unable to find anything from which we can reason- 
ably conclude that he prefers the one cause to the other. It 
would seem that he regards both as real causes, and that he 
has faQed to perceive that the one is destructive of the other. 
But it is difficult to conceive how he could believe that the sea 
in equatorial regions, by virtue of its higher temperature, is 
lighter than the sea in polar regions, while at the same time it 
M not lighter but heavier, in consequence of its greater saltness 
—how he could believe that the warm water at the equator 
flows to the poles as an upper current, and the cold water at 



no CLIMATE AND TIME. 

the poles to the equator as an under current^ while at the same 
time the warm water at the equator does not flow to the poles 
as a surface current, nor the cold water at the poles to the 
equator as an under current, but the reyerse. And yet, unless 
these absolute impossibilities be possible, how can an ocean- 
cuiTent be the result of both causes P 

The only explanation of the matter appears to be that Maury 
has failed to perceive the contradictory nature of his two 
theories. This fact is particularly seen when he comes to apply 
his two theories to the case of the Gulf-stream. He maintains, 
as has already been stated, that the waters of the Gulf-stream 
are solter than the waters of the sea through which they flow 
(see §§ 3, 28, 29, 30, 34, and several other places). And he states, 
as we have already seen (see p. 104), that the existence of the 
Gulf stream is due principally to the difference of density of 
the water of the Caribbean Sea and the Gulf of Mexico as 
compared with that of the great Polar Basin and the North Sea. 
There can be no doubt whatever that it is the density of the 
waters of the Gulf-stream at its fountain-head, the Gulf of 
Mexico, resulting from its superior saltness, and the deficiency of 
density of the waters in polar regions and the North Sea, &c., that 
is here considered to be unmasked as one of the agents. If this 
be a cause of the motion of the Gulf-stream, how then can the 
difference of temperature between the waters of inter-tropical 
and polar regions assist as a cause ? This difference of tem- 
perature will simply tend to undo all that has been done by 
difference of saltness : for it will tend to make the waters of 
the Ghilf of Mexico lighter, and the waters of the polar regions 
heavier. But Maury maintains, as we have seen, that this 
difference of temperature is also a cause, which shows that he 
does not perceive the contradiction. 

This is still further apparent. He holds, as stated, that '' the 
waters of the Gulf-stream are Salter than the waters of the sea 
through which they flow," and that this excess in saltness, by 
Tn^Ving the water heavier, is a cause of the motion of the 
But he maintains that, notwithstanding the ^ect 



THE GRA VITA TION THEORY. 1 1 1 

which greater saltness has in increasing the density of the 
waters of the Golf-stream, yet, owing to their higher tempera- 
tnrOy ihey are actually lighter than the water through which 
they flow ; and as a proof that this is the case, he adduces 
the £sust that the sur&ce of the Gulf-stream is roof-shaped 
(§§ 39 — 41), which it could not be were its waters not actually 
lighter than the waters through which the stream flows. So 
it turns out that, in contradiction to what he had already 
stated, it is the lesser density of the waters of the Gulf- 
stream that is the real cause of their motion. The greater 
saltness of the waters, to which he attributes so much, can 
in no way be regarded as a cause of motion. Its efiect, so 
far as it goes, is to stop the motion of the stream rather than to 
assist it. 

But, again, although he asserts that diflerence of saltness 
and difference of temperature are both causes of ocean-currents, 
yet he appears actually to admit that temperature and saltness 
neutralize each other so as to prevent change in the specific 
gravity of the ocean, as will be seen from the following 
quotation : — 

'^ It is the trade- winds, then, which prevent the thermal and 
specific-gravity curves from conforming with each other in inter- 
tropical seas. The water they suck up is fresh water ; and the 
salt it contained, being left behind, is just sufficient to counter- 
balance, by its weight, the efiect of thermal dilatation upon the 
specific gravity of sea-water between the parallek of 34^ north 
and south. As we go from 34^ to the equator, the water grows 
warmer and expands. It would become lighter ; but the trade- 
winds, by taking up vapour without salt, make the water Salter, 
and therefore heavier. The conclusion is, the proportion of 
salt in sea-water, its expansibility between 62° and 82°, and 
the thirst of the trade-winds for vapour are, where they blow, 
so balanced as to produce perfect compensation ; and a more 
beautiful compensation cannot, it api>ears to me, be found in 
the mechanism of the universe than that which we have here 
stumbled upon. It is a triple adjustment ; the power of the 



xia CLIMATE AND TIME. 

mm to expand, the power of the winds to eTaporate, and the 
quantity of salts in the sea — these are so proportioned and 
adjusted that when both the wind and the sun have each 
played with its forces upon the inter-tropical waters of the 
ocean, the residuum of heat cmd of salt shoidd he Just 9uch as 
to balance ea4ih other in th^i/r effects; and so the aqueous e^pnltlh 
rium of the torrid zone is preserved^^ (§436, eleventh edition). 

" Between 35° or 40° and the equator evaporation is in excess 
of precipitation ; and though, as we approach the equator on 
either side from these parallels, the solar ray warms and ex- 
pands the surface-water of the sea, the winds, by the vapour 
they carry off, and the salt they leave behind, prevent it from 
making that water lighter " (§ 437, eleventh edition). 

" Philosophers have admired the relations between the size 
of the earth, the force of gravity, and the strength of fibre in 
the flower-stalks of plants ; but how much more exquisite is 
the system of counterpoises and adjustments here presented 
between the sea and its salts, the winds and the heat of the 
sun 1 " (§ 438, eleventh edition). 

How can this be reconciled with all that precedes regarding 
ocean-currents being the result of difference of specific gravity 
caused by a difference of temperature and difference of salt- 
ness ? Here is a distinct recognition of the fact that difference 
in saltness, instead of producing currents, tends rather to pre- 
vent the existence of currents, by counteracting the effects of 
difference in temperature. And so effectually does it do this, 
that for 40°, or nearly 3,000 miles, on each side of the equator 
there is absolutely no difference in the specific gravity of the 
ocean, and consequently nothing, either as regards difference 
of temperature or difference of saltness, that can possibly give 
rise to a current. 

But it is evident that, if between the equator and latitude 
Aff the two effects completely neutralize each other, it is not at 
all likely that between latitude 40° and the poles they will not 
to a lai^ extent do the same thing. And if so, how can 
MeaafCarreiiti be due either to difference in temperature or to 



THE GRA VITATION THEORY. 113 

in saltnessy £ar leas to both. If there be any differ- 
ence of specific grayity of the ocean between latitude 40"^ and 
the poles, it mnst be only to the extent by which the one cause 
has fiuled to neutralize the other. If^ for example, the waters 
in latitude 40^, by Tirtue of higher temperature, are less dense 
than the waters in the polar regions, they can be so only to the 
extent that difference in saltness has failed to neutralize the 
effect of difference in temperature. And if currents result, they 
can do so only to the extent that difference in saltness has thus 
fallen short of being able to produce complete compensation. 
Maury, after stating his views on compensation, seems to 
become aware of this ; but, strangely, he does not appear to 
perceive, or, at least, he does not make any allusion to the fact, 
that all this is fatal to his theories about ocean-currents being 
the combined result of differences of temperature and of salt- 
ness. For, in opposition to all that he had previously advanced 
regarding the difficulty of finding a cause sufficiently powerful 
to account for such currents as the Gulf-stream, and the great 
importance that difference in saltness had in their production, he 
now begins to maintain that so great is the influence of differ- 
ence in temperature that difference in saltness, and a number of 
other compensating causes are actually necessary to prevent the 
ocean-currents from becoming too powerful. 

" If all the inter- tropical heat of the sun," he says, " were to 
pass into the seas upon which it falls, simply raising the tem- 
perature of their waters, it would create a thermo- dynamical 
force in the ocean capable of transporting water scalding hot 
from the torrid zone, and spreadiilg it while still in the tepid 
state aroxmd the poles .... Now, suppose there were no 
trade-winds to evaporate and to counteract the dynamical force 
of the sun, this hot and light water, by becoming hotter and 
lighter, would flow off in currents with almost mill-tail velocity 
towards the poles, covering the intervening sea with a mantle 
of warmth as a garment. The cool and heavy water of the 
polar basin, coming out as under currents, would flow equa- 
torially with equal velocity.'' 



ii4 



CLIMATE AND TIME. 



** Thus two antagonistic forces are unmasked, and, being un- 
masked, we discover in them a most exquisite adjustment-— a 
compensation — ^by which the dynamical forces that reside in 
the sunbeam and the trade- wind are made to counterbalance 
each other, by which the climates of inter-tropical seas are 
regulated, and by which the set, force, and volume of oceanic 
currents are measured '* (§§ 437 and 438, eleventh edition). 



CHAPTER Vn. 

EXAMINATION OF THB ORATITATION THEORY OF OCEANIC COUJU* 
LATION. ^LIBUT. MAURT^S THEORY (continued). 

Methods of determining the Qaestion. — ^The Foroe resulting from Difference of 
Specific Gravity. — Sir John Henchel's Estimate of the Force.— rMazimnm 
Density of Sea- Water. — Bate of Decrease of Temperature of Ocean at 
Eqnator. — The actual Amount of Force resulting from Ditference of Specific 
Grayity. — M. Duhoat's Experiments. 

Sotc the Question maybe Determined. — ^Whether the circulation 
of the ocean is due to difference in specific gravity or not may 
be determined in three ways : viz. (1) by direct experiment ; 
(2) by ascertaining the absolute amount oi force acting on the 
water to produce motion^ in virtue of difference of specific 
gravity, and thereafter comparing it with the force which has 
been ^own by experiment to be necessary tc the production of 
sensible motion ; or (3) by determining the greatest possible 
amount of work which gravity can perform on the waters in 
virtue of difference of specific gravity, and then ascertaining if 
the work of gravity does or does not equal the work of the 
resistances in the required motion. But Maury has not adopted 
either of these methods. 

The Force resulting from Difference of Specific Gravity. — I shall 
consider first whether the force resulting from difference of 
specific gravity be sufficient to account for the motion of ocean- 
currents. 

The inadequacy of this cause has been so clearly shown by 
Sir John Herschel, that one might expect that little else would 
be required than simply to quote his words on the subject, 
which are as follows : — 

"First, then, if there were no atmosphere, there would be no 



ii6 CLIMATE AND TIME. 

Gulf-stream, or any other considerable ocean-current (as distin* 
guished from a mere surface-drift) whatever. By the action oi 
the sun's rays, the surface of the ocean becomes most heated, and 
the heated water will, therefore, neither directly tend to ascend 
(which it could not do without leaving the sea) nor to descend^ 
which it cannot do, being rendered buoyant, nor to move late- 
rally, no lateral impulse being given, and which it could only 
do by reason of a general declivity of surface, the dilated por- 
tion occupying a higher level. Let us see what this declivity 
would amount to. The equatorial surface-water has a tempe- 
rature of 84°. At 7,200 feet deep the temperature is 39°, the 
level of which temperature rises to the surface in latitude 56°. 
Taking the dilatability of sea- water to be the same as that of fresh, 
a uniformly progressive increase of temperature, from 39° to 84° 
Fahr., would dilate a column of 7,200 feet by 10 feet, to which 
height, therefore, above the spheroid of equilibrium (or above 
the sea-level in lat. 56°), the equatorial surface is actually raised 
by dilatation. An arc of 56° on the earth's surface measures 
3,360 geographical miles ; so that we have a slope of l-28th of 
an inch per geographical mile, or l-32nd of an inch per statute 
mile for the water so raised to run down. As the accelerating 
force corresponding to such a slope (of 1-lOth of a second, 0"'l) 
is less than one two-millionth part of gravity, we may dismiss 
this as a cause capable of creating only a very trifling surface- 
drift, and not worth considering, even were it in the proper 
direction to form, by concentration, a current from east to west, 
which it icould not be, but the very reverse J^ * 

It is singular how any one, even though he regarded this 
conclusion as but a rough approximation to the truth, could 
entertain the idea that ocean-currents can be the result of 
dijQTerence in specific gravity. iTiere are one or two reasons, 
however, which may be given for the above not having been 
generally received as conclusive. Herschel's calculations refer 
to the diflference of gravity resulting from difference of tempe- 
rature ; but this is only one of the causes to which Maury 

♦ " Physical Geography/' article 67, 




THE GRAVITATION THEORY. 



"7 



appeals, and even not the one to whicH he most frequently 
refers. He insists so strongly on the effects of difference of 
saltness, that many might think that, although Herschel may 
have shown that difference in specific gravity arising from 
difference of temperature could not account for the motion of 
ocean-currents, yet neyertheless that this, combined with the 
effects resulting from difference in saltness, might be a sufficient 
explanation of the phenomena. Such, of course, would not be 
the case with those who perceived the contradictory nature of 
Maury's two causes ; but probably many read the " Physical 
Greography of the Sea '' without being aware that the one cause 
is destructive of the other. Again, a few plausible objections, 
which have never received due consideration, have been strongly 
urged by Maury and others against the theory that ocean- 
currents can be caused by the impulses of the winds; and 
probably these objections appear to militate as strongly against 
his theory as Herschel's arguments against Maury's. 

There is one trifling objection to Herschel's result : he takes 
39^ as the temperature of maximum density. This, however, 
as we shall see, does not materially affect his conclusions. 

Observations on the temperature of the maximum density of 
sea-water have been made by Erman, Despretz, Rossetti, Neu- 
mann, Marcet, Hubbard, Homer, and others. No two of them 
have arrived at exactly the same conclusion. This probably 
arises from the fact that the temperature of maximum density 
depends upon the amount of salt held in solution. No two seas, 
unless they are equal as to saltness, have the same temperature of 
maximum density. The following Table of Despretz will show 
how rapidly the temperature of both the freezing-point and of 
maximum density is lowered by additional amounts of salt :— 



AmoimtofaJi. 


Tem^rfttare of 
freenng^point. 


Temperature of \ 


0000123 
00246 
00371 
0*0741 


-i-21 a 

-2-24 
-2-77 
-6-28 


+ 119 0. 

- 1-69 

- 4-76 
-1600 



ii8 CLIMATE AND TIME. 

He found the temperature of maximum density of sea- water, 
whose density at 20°C. was 10273, to be — 3°-67C. (25°-4F.), 
and the temperature of freezing-point — ^2°'55 (27°*4F.).* Some- 
where between 25^ and 26^ F. may therefore be regarded as 
the temperature of maximum density of sea-water of average 
saltness. We have no reason to believe that the ocean, from 
the surface to the bottom, even at the poles, is at 27^*4 F., the 
freezing-point. 

The actual slope resulting from difference of specific gravity, 
as we shall presently see, does not amount to 10 feet. Herschel's 
estimate was, however, made on insufficient data, both as to 
the rate of expansion of sea- water and that at which the tem- 
perature of the ocean at the equator decreases from the sur&ce 
downwards. We are happily now in the possession of data for 
determining with tolerable accuracy the amount of slope due 
to difference of temperature between the equatorial and polar 
seas. The rate of expansion of sea-water from 0°C. to lOO^C. 
has been experimentally determined by Professor Muncke, of 
Heidelberg, t The valuable reports of Captain Nares, of H.M.S. 
Challenger y lately published by the Admiralty, give the rate at 
which the temperature of the Atlantic at the equator decreases 
from the surface downwards. These observations show clearly 
that the super-heating effect of the sun's rays does not extend 
to any great depth. They also prove that at the equator the 
temperature decreases as the depth increases so rapidly that at 
60 fathoms from the surface the temperature is 62°'4, the same 
as at Madeira at the same depth ; while at the depth of 150 
fathoms it is only 51^, about the same as that in the Bay of 
Biscay (Reports, p. 11). Here at the very outset we have broad 
and important facts hostile to the theory of a flow of water 
resulting from difference of temperature between the ocean iii 
equatorial and temperate and polar regions. 

Through the kindness of Staff-Captain Evans, Hydrographer 

* Philosophiciil Ma^^azine, vol. xii. p. 1 (1838). 

t "Memoires par divers Savans," torn, i., p. 318, St. Petereburgli, 1881. 8e« 
also twelftn number of Meteorological Papers, published by the Board of Trader 
IM6, p. 16. 



THE GRAVITATION THEORY. 



ii9 



of the Admiralty, I tiaye been favoured with a most valuable 
aet of aerial temperature soundings made by Captain Nares of 
the ChaUengefy close to the equator, between long. 14° 49^ W. 
and 32° 16' W. The following Table represents the mean of 
the whole of these observations : — 



fktfaoms. 


Tempera- 
ture. 


Fathoms. 


Tempera- 
ture. 


FkthomB. 


Tempera- 
ture. 


Suiface. 


77-9 


90 


68-0 


800 


39°1 


10 


77-2 


100 


66-6 


900 


38-2 


20 


771 


150 


610 


1000 


36-9 


30 


76-9 


200 


46-6 


1100 


37-6 


40 


71-7 


300 


42-2 


1200 


36 7 


60 


640 


400 


40-3 


1300 


86-8 


60 


60-4 


600 


38-9 


14U0 


36-4 


70 


69-4 


600 


39-2 


1600 


361 


80 


680 

1 


700 


390 


Bottom. 


34-7 



We have in this Table data for determining the height at 
which the surface of the ocean at the equator ought to stand 
above that of the poles. Assuming 32^ F. to be the tempera- 
ture of the ocean at the poles from the surface to the bottom 
and the foregoing to be the rate at which the temperature of 
the ocean at the equator decreases from the surface downwards, 
and then calculating according to Muncke's Table of the ex- 
pansion of sea-water, we have only 4 feet 6 inches as the height 
to which the level of the ocean at the equator ought to stand 
above that at the poles in order that the ocean may be in static 
equilibrium. In other words, the equatorial column requires to 
be only 4 feet 6 inches higher than the polar in order that the 
two may balance each other. 

Taking the distance from the equator to the poles at 6,200 
miles, the force resulting from the slope of 4 J feet in 6,200 
will amount to only l-7,340,000th that of gravity, or about 
1 -1000th of a grain on a pound of water. But, as we shall shortly 
see, there can be no permanent current resulting from difference 
of temperature while the two columns remain in equilibrium, 
for the current is simply an effort to the retardation of equiii- 



lao CLIMATE AND TIME. 

brium. In order to permanent circnlation there must be a 
permanent disturbance of equilibrium. Or, in other words, the 
weight of the polar column must be kept in excess of that of 
the equatorial. Suppose, then, that the weight of the polar 
column exceeds that of the equatorial by 2 feet of water, the 
difference of level between the two columns will, in that case, 
amount to only 2 feet 6 inches. This would give a force of only 
l-13,200,000th that of gravity, or not much over l-l,900th of a 
grain on a pound of water, tending to draw the water down 
the slope from the equator to the poles, a force which does 
not much exceed the weight of a grain on a ton of water. But 
it must be observed that this force of a grain per ton would 
affect only the water at the surface ; a very short distance 
below the surface the force, small as it is, would be enormously 
reduced. If water were a perfect fluid, and offered no resistance 
to motion, it would not only flow down an incline, however small 
it might be, but would flow down with an accelerated motion. 
But water is not a perfect fluid, and its njolecules do offer con- 
siderable resistance to motion. "Water flowing down an incline, 
however steep it may be, soon acquires a uniform motion. 
There must therefore be a certain inclination below which no 
motion can take place. Experiments were made by M. Dubuat 
with the view of determining this limit.* He found that when 
the inclination was 1 in 500,000, the motion of the water was 
barely perceptible ; and he came to the conclusion that when 
the inclination is reduced to 1 in 1,000,000, all motion ceases. 
But the inclination afforded by the difference of temperature 
between the sea in equatorial and polar regions does not amount 
to one-seventh of this, and consequently it can hardly produce 
even that " trifling surface-drift *' which Sir John Hcrschel is 
willing to attribute to it. 

There is an error into which some writers appear to fall to 
which I may here refer. Suppose that at the equator we have 
to descend 10,000 feet before water equal in density to that at 

• ]>almat'i « Hjdnnliqne," torn, i., p. 64 (1816). See also British 
te 1834, pp. 422, 461. 




THE GRAVITATION THEORY, 



121 



the poles is reached. We have in this case a plain with a slope 
of 10,000 feet in 6,200 miles, forming the upper surface of the 
water of maximum density. Kow this slope exercises no influ- 
ence in the way of producing a current, as some seem to think ; 
for it is not a case of disturbed equilibrium, but the reverse. 
It is the condition of static equilibrium resulting from a differ- 
ence between the temperature of the water at the equator and 
the poles. The only slope that has any tendency to produce 
motion is that which is formed by the surface of the ocean in 
the equatorial regions being higher than the surface at the 
poles ; but this is an inclination of only 4 feet 6 inches, and is 
therefore wholly inadequate to produce such currents as the 
Gulf-streanL 



CHAPTER VIII. 

EXAMINATION OF THE GRAVITATION THEORY OF OCE.\NIO 
CIRCULATION. DR. CARPENTER's THEORY. 

Ghiff-stream according to Br. Carpenter not due to Difiference of Specific GrmTitf. 
— Facts to be Explained. — ^The Explanation of the Facts. — ^The EzplanatioQ 
hypothetical. — ^The Cause assigned for the hypothetical Mode of Cirool*- 
tion. — Under currents account for all the Facts better than the Gravitation 
Hypothesis. — Known Condition of the Ocean inconsistent with that Hypo- 
thesis. 

Dh. Carpenter does not suppose, with Lieut. Maury, that the 
difference of temperature between the ocean in equatorial and 
polar regions can account for the Gulf-stream and other great 
cur ents of the ocean. He maintains, however, that this differ- 
ence is quite sufficient to bring about a slow general inter- 
change of water between the polar and inter-tropical areas — ^to 
induce a general movement of the upper portion of the ocean 
from the equator to the poles and a counter-movement of the 
under portion in a contrary direction. It is this general move- 
ment which, according to that author, is the great agent by 
which heat is distributed over the globe.* 

In attempting to estimate the adequacy of this hypothesis as 
an explanation of the phenomena involved, there are obvioualy 
two questions to be considered : namely, (1) is the difference of 
temperature between the sea in inter-tropical and polar regions 
sufficiently great to produce the required movement ? and (2) 
assuming that there is such a movement, does it convey the 
amount of heat which Dr. Carpenter supposes ? I shall begin 
with the consideration of the first of these two points. 

• See Prr»ce€din!r« of the R^yal Society for December, 18G8, Korcmber, 
1869. Lecturt* deliv^ed at the Royal Jn^titnte, Xaturf, vol. i.. p. 490 
of the Royal Geographical Society, vol. xv. 




THE GRA VITA TION THEORY. 1 2 3 

But before doing so let us see what the fuct« are which this 
gravitation theory is intended to expkin. 

The Facts to be Explained, — Dr. Carpenter considers that the 
gipat mass of warm water proved during recent dredging expe- 
ditions to occupy the depths of the North Atlantic, must be 
referred, not to the Ghilf-stream, but to a general movement'* . 
water from the equator. " The inference seems inevitable/' 
he says, ^' that the bulk of the water in the warm area must 
have come thither from the south-west. The influence of the 
Gulf-stream proper (meaning by this the body of superheated 
water which issues through the ' Narrows ' from the Gulf of 
Mexico), if it reaches this locality at all (which is very 
doubtful), could only affect the moat superficial stratum ; and 
the same may be said of the surface- drift caused by the pre- 
valence of south-westerly winds, to which some have attributed 
the phenomena usually accounted for by the extension of the 
Gulf-stream to these regions. And the presence of the body of 
water which lies between 100 and 600 fathoms deep, and the 
range of whose temperature is from 48° to 42°, can scarcely be 
accounted for on any other hypothesis than that of a great 
general moceiuent of equatorial tcater toiainh the polar area, 01 
which movement the Gulf-stream constitutes a peculiar case 
modified by local conditions. In like manner the Arctic stream 
which underlies the warm superficial stratum in our cold area 
constituted a peculiar case, modified by the local conditions to 
be presently explained, of a great general movement of polar 
tcater toxcards the equatorial area, which depresses the tempera- 
ture of the deepest parts of the great oceanic basins nearly to 
the freezing-point." 

It is well-known that, wherever temperature-observations 
have been made in the Atlantic, the bottom of that ocean has 
been found to be occupied by water of an ice-cold temperature. 
And this holds true not merely of the Atlantic, but also of the 
ocean in inter-tropical regions — a fact which has been proved 
by repeated observations, and more particularly of late by those 
of Commander Chimmo in the China Sea and Indian Ocean, 



124 CLIMATE AND TIME. 

where a temperature as low as 32^ Fabr. was found at a depth 
of 2,656 fathoms. In short, the North Atlantic, and probably 
the inter-tropical seas also, may be regarded. Dr. Carpenter 
considers, as divided horizontally into two great layers or 
strata — ^an upper warm, and a lower cold stratum. All these 
facts I, of course, freely admit ; nor am I aware that their 
truth has been callod in question by any one, no matter what 
his views may have been as to the mode in which they are to 
be explained. 

The Explanation of the Facts. — We have next the explanation 
of the facts, which is simply this : — The cold water occupying 
the bottom of the Atlantic and of inter-tropical seas is to be 
accounted for by the supposition that it came from the polar 
regions. This is obvious, because the cold possessed by the 
water could not have been derived from the crust of the earth 
beneath : neither could it have come from the surface ; for the 
temperature of the bottom water is fur below the normal tem- 
perature of the latitude in which it is found. Consequently 
** the inference seems irresistible that this depression must be 
produced and maintained by the convection of cold from the 
polar towards the equatorial area." Of course, if we suppose a 
flow of water from the poles towards the equator, we must 
necessarily infer a counter flow from the equator towards the 
poles ; and while the water flowing from equatorial to polar 
regions \iill be tcarm, that flowing from polar to equatorial 
regions will be cold. The doctrine of a mutual interchange of 
equatorial and polar water is therefore a necessary consequence 
from the admission of the foregoing facts. With this expUi" 
nation of the farts I need hardly say that I fully agree; nor am 
I aware that its correctness has ever been disputed. Dr. Car- 
penter surely cannot charge mo with overlooking the fact of a 
mutual interchange of equatorial and polar water, seeing that 
my estimate of the thermal power of the Gulf- stream, from 
which it is proved that the amount of heat conveyed from 
equatorial to temperate and polar regions is enormously g^reater 
than had ever been anticipated, was made a considerable time 



THE GRA VITATION THEORY. 125 

before he began to write on the subject of oceanic circulation.* 
And in my paper '' On Ocean-currents in relation to the Dis- 
tribation of Heat over the Globe " f (the substance of which 
is reproduced in Chapters II. and III. of this yolume), I have 
endeaTOured to show that, were it not for the raising of the 
temperature of polar and high temperate regions and the 
lowering of the temperature of inter-tropical regions by means 
of this interchange of water, these portions of the globe would 
not be habitable by the present existing orders of beings. 

The explanation goes further : — '' It is along the surface and 
upper portion of the ocean that the equatorial waters flow 
towards the poles, and it is along the bottom and under portion 
of the ocean that polar waters flow towards the equator ; or, in 
other words, the warm water keeps the upper portion of the 
ocean and the cold water the under portion.'* With this 
explanation I to a great extent agree. It is evident that, in 
reference to the northern hemisphere at least, the most of the 
water which flows from inter-tropical to polar regions (as, for 
example, the Gulf-stream) keeps to the surface and upper 
portion of the ocean ; but for reasons which I have already 
stated, a very large proportion of this water must return in the 
form of under currents ; or, which is the same thing, the return 
compensating current, whether it consist of the identical water 
which originally came from the equator or not, must flow 
towards the equator as an under current. That the cold water 
which is found at the bottom of the Atlantic and of inter- 
tropical seas must have come as under currents is perfectly 
obvious, because water which should come along the surface 
of the ocean from the polar regions would not be cold when it 
reached inter-tropical regi(ms. 

The Explanation hypotheticaL — Here the general agreement 
between us in a great measure terminates, for Dr. Carpenter is 
not satisfied with the explanation generally adopted by the 

• Trans, of Glasgow Gcol. Soo. for Apiil, 1867. Phil. Mng. for Februaxy, 
1S67, and June, 1867. 
t Pha. Mag. for February, 1870. 



1/b CLIMATE AND TIME. 

advocates of the wind theory ^ tiz.^ that the cold water found in 
temperate and inter-tropical areas comes from polar regions as 
compensating under currents, but advances a hypothetical form 
of circulation to account for the phenomenon. He assumes that 
there is a general set or flow of the sur&ce and upper portion of 
the ocean from the equator to polar regions, and a general set or 
flow of the bottom and imder portion of the ocean from polar 
regions to the equator. Mr. Ferrel {Nature, June 13, 1872) 
speaks of that *' interchanging motion of the water between the 
equator and the pole discovered by Dr. Carpenter.'' In this, 
however, Mr. Ferrel is mistaken ; for Dr. Carpenter not only 
makes no claim to any discovery of the kind, but distinctly 
admits that none such has yet been made. Although in some 
of his papers he speak^ of a " set of warm surface-water in the 
southern oceans toward the Antarctic pole " as being well known 
to navigators, yet he nowhere affirms, as far as I know, that the 
existence of such a general oceanic circulation as he advocates 
has ever been directly determined from observations. This 
mode of circulation is simply inferred or assumed in order to 
account for the facts referred to above. " At present," Dr. 
Carpenter says, ** I claim for it no higher character than that 
of a good working hypothesis to be used as a guide in further 
inquiry*' (§ 16) ; and lest there should be any misapprehension 
on this point, he closes his memoir thus : — ** At present, as I 
have already said, I claim for the doctrine of a general oceanio 
circulation no higher a character than that of a good working 
hypothesis consistent with our present knowledge of facts, and 
therefore entitled to be provisionally adopted for the purpose of 
stimulating and directing further inquiry." 

I am unable to agree with him, however, on this latter point. 
It seems to me that there is no necessity for adopting any 
hypothetical mode of circulation to account for the facts, as they 
can be quite well accounted for by means of that mode of cir- 
culation which does actually exist. It has been determined from 
direct observation that surface-currents flow from equatorial to 
polar regions, and their paths have been actually mapped out 



THE GRA VITA TION THEORY. 1 27 

But if it is established tliat cnrrents flow from equatorial to 
polar regions, it is equally so that return currents flow from 
polar to equatorial regions ; for if the one actually exists, the 
other of necessity must exist. We know also on physical 
grounds, to which I have already referred, and wliich fall to 
be considered more fully in a subsequent chapter, that a very 
large portion of the water flowing from polar to equatorial 
regions must be in the form of under currents. If there are 
cold nnder currents, therefore, flowing from polar to tem- 
perate and equatorial regions, this is all that we really require 
to accoimt for the cold water which is found to occupy the bed 
of the ocean in those regions. It does not necessarily follow, 
because cold water may be found at the bottom of the ocean all 
along the eqnator, that there must be a direct flow from the 
polar regions to every point of the equator. Water brought 
constantly from the polar regions to various points along the 
equator by means of under currents will necessarily accumulate, 
and in course of time spread over the bottom of the inter- 
tropical seas. It must either do this, or the currents on 
reaching the equator must bend upwards and flow to the 
surface in an unbroken mass. Considerable portions of some 
of those currents may no doubt do so and join surface-currents ; 
but probably the greater portion of the water coming from 
polar regions extends itself over the floor of the equatorial seas. 
In a letter in Nature^ January 11, 1872, I endeavoured to show 
that the surface-currents of the ocean are not separate and 
independent of one another, but form one grand system of 
circulation, and that the impelling cause keeping up this 
system of circulation is not the trade- winds alone, as is generally 
supposed, but the prevailing mnds of the entire globe considered 
also as one grrnid system. The evidence for this opinion, how- 
ever, will be considered more fully in the sequel. 

Although the under currents are parts of one general system 
of oceanic circulation produced by the impulse of the system of 
prevailing winds, yet their direction and position are never- 
theless, to a large extent, determined by difierent laws. The 

7 



128 CLIMATE AND TIME. 

water at the surface, being moved by the force of the wind| 
will follow the path of greatest pressure and traction, — the efiPects 
resulting from the general contour of the land, which to a 
great extent are common to both sets of currents, not being 
taken into account; while, en the other hand, the under 
currents from polar regions (which to a great extent are simply 
" indraughts '* compensating for the water drained from equa- 
torial regions by the Gidf-stream and other surface current^i) 
will follow, as a general ride, the path of least resistance. 

The Cause assigned for the Hgpothetical Mod^ of Circulation. — 
Dr. Carpenter assigns a cause for his mode of circulation ; and 
that cause he finds in the difference of specific gravity between 
equatorial and polar waters, resulting from the difference of 
temperature between these two regions. ** Two separate ques- 
tions," he says, " have to be considered, which have not, 
perhaps, been kept sufficiently distinct, either by Mr. Croll or 
by myself; — -Jirst, whether there is adequate evidence of the 
existence of a general vertical oceanic circulation ; and second, 
whether, supposing its existence to be provisionally admitted, a 
vera causa can be found for it in the difference of temperature 
between the oceanic waters of the polar and equatorial areas " 
(§ 17). It seems to me that the facts adduced by Dr. Carpenter 
do not necessarily require the assumption of any such mode of 
circidation as that advanced by him. The phenomena can be 
satisfactorily accounted for otherwise ; and therefore there does 
not appear to be any necessity for considering whether his 
hypothesis be sufficient to produce the required effect or not. 

An important Consideration overlooked, — But there is one 
important consideration which seems to have been overlooked 
— namely, the fact that the sea is salter in inter-tropical than 
in polar regions, and that this circumstance, so far as it goes, 
must tend to neutralize the effect of difference of temperature. 
It is probable, indeed, that the effect produced by difierence of 
temperature is thus entirely neutralized, and that no difference 
of density whatever exists between the sea in inter-tropical and 
polar regions, and consequently that there is no difference of 



THE GRAVITATION THEORY, 129 

level nor anything to produce such a general motion as Dr. 
Carpenter supposes. This, I am glad to find, is the opinion of 
Professor Wyville Thomson. 

"I am greatly mistaken/' says that author, "if the low 
specific gravity of the polar sea, the result of the condensation 
and precipitation of vapour evaporated from the inter-tropical 
area, do not fully counterbalance the contraction of the super- 
ficial film by arctic cold. . . . Speaking in the total absence of 
all reliable data, it is my general impression that if we were to 
set aside all other agencies, and to trust for an oceanic circula- 
tion to those conditions only which are relied upon by Dr. 
Carpenter, if there were any general circulation at all, which 
seems very problematical, the odds are rather in favour of a 
warm under current travelling northwards by virtue of its 
excess of salt, balanced by a surface return current of fresher 
though colder arctic water." * 

This is what actually takes place on the west and north-west 
of Spitzbergen. There the warm water of the Gulf-stream 
flows underneath the cold polar current. And it is the opinion 
of Dr. Scoresby, Mr. Clements Markham, and Lieut. Maury 
that this warm water, in virtue of its greater saltness, is denser 
than the polar water. Mr. Leigh Smith found on the north- 
west of Spitzbergen the temperature at 500 fathoms to be 52°, 
and once even 64°, while the water on the surface was only a 
degree or two above freezing. t Mr. Aitken, of Darroch, in a 
paper lately read before the Royal Scottish Society of Arts, 
showed experimentally that the polar water in regions where 
the ice is melting is actually less dense than the warm and more 
salt tropical waters. Nor will it help the matter in the least to 
maintain that difference of specific gravity is not the reason 
why the warm water of the Gulf-stream passes under the polar 
stream — because if difference of specific gravity be not the 
cause of the warm water underlying the cold water in polar 
regions, then difference of specific gravity may likewise not 

• " The "Depths of the Sea," pp. 376 and 377. 

t "The ThieHhold of the Unknown Region," p. 95. 



i)o CLIMATE AND TIME. 

be the cause of the cold water underlying the warm at the 
equator ; and if so, then there is no necessity for the gravita* 
tion hypothesis of oceanic circulation. 

There is little doubt that the super-heated stratum at the 
surface of the inter-trcpical seas, which stratum, according to 
Dr* Carpcnt<*r, is of no great thickness, is less dense than the 
polar water: but if we take a column extending from the 
surface down to the bottom of the ocean, this column at the 
equator will bo found to be as heavy as one of equal length in 
the polar area. And if this be the case, then there can be no 
difference of level between the equator and the poles, and no 
disturbance of static equilibrium nor anything else to produce 
circulation. 

Under Currents account for all the Facts better than Dr, Car^ 
pcntcr^H Hypothesis, — Assuming, for the present, the system of 
prevailing winds to be the true cause of oceanic currents, it 
neccHsarily follows (as will bo shown hereafter) that a large 
quantity of Atlantic water must be propelled into the Arctic 
Ocean ; and such, as we know, is actually the cose. The 
Arctic Ocean, however, as Professor Wyville Thomson remarksi 
is a well-ni^h closed basin, not permitting of a free outflow 
into the raeilic Ocean of the water impelled into it. 

Ihit it is evident that the water which is thus being con- 
stantly earritnl from the in tor- tropical to the arctic regions 
must somehow or other find its way back to the equator ; in 
other words, there must be a return current equal in magnitude 
to the dirwt current. Now the question to be determined is^ 
what path must this return current take? It appears tome 
that it will t-ako the path of least resistance, whether that path 
may happen to be at the surface or under the surfiice. But 
that the path of least rosiistance will, as a general rule, lie 
at a very eonsldeniblo divst:ince below the suriace is, I think, 
evident fnun the following considerations. At the surface 
the gtmeral direetion of the currents is opposite to that of the 
rt^turn eurront. The surface motion of the water in th(» Atlantic 
ia from the tnju itor to the p >le ; but the return eur'vnt must be 



THE GRAVITATION THEORY. iji 

from the pole to the equator. Consequently the surface currents 
will oppose the motion of any return current unless that current 
Ue at a considerable depth below the surface currents. Again, 
the winds, as a general rule, blow in an opposite direction to 
the course of the return current, because, according to supposi- 
tion, the winds blow in the direction of the surface currents. 
From all these causes the path of least resistance to the return 
current will, as a general rule, not bo at the surface, but at a 
very considerable depth below it. 

A large portion of the water from the polar regions no doubt 
leaves those regions as surfieuse currents ; but a surface current 
of this kind, on meeting with some resistance to its onward 
progress along the surface, will dip down and continue its 
course as an under current. We have an example of this in 
the case of the polar current, which upon meeting the Gulf- 
stream on the banks of Newfoundland divides — ^a portion of it 
dipping down and pursuing its course imdemeath that stream 
into the Gulf of Mexico and the Caribbean Sea. And that this 
under current is a real and tangible current, in the proper 
sense of the term, and not an imperceptible movement of the 
water, is proved by the fact that large icebergs deeply immersed 
in it are often carried southward with considerable velocity 
against the imited force of the wind and the Gulf-stream. 

Dr. Carpenter refers at considerable length (§ 134) to Mr. 
Mitchell's opinion as to the origin of the polar current, which 
is the same as that advanced by Maury, viz., that the impelling 
cause is difference of specific gravity. But although Dr. Car- 
penter quotes Mr. Mitchell's opinion, he nevertheless does not 
appear to adopt it : for in §§ 90-93 and various other places he 
distinctly states that ho does not agree with Lieut. Maury's 
view that the Gulf-stream and polar current are caused by 
difference of density. In fact, Dr. Carpenter seems particularly 
anxious that it should be clearly understood that he dissents 
from the theory maintained by Maury. But he does not 
merely deny that the Gulf-stream and polar current can be 
caused by difference of density; ho even goes so far as to 



132 CLIMATE AND TIME. 

affirm that no sensible current whateTer can be due to tbat 
cause, and adduces the authority of Sir John Herschel in sup- 
port of that opinion : — " The doctrine of Lieut. Maury," he 
says, " was powerfully and convincingly opposed by Sir John 
Herschel ; who showed, beyond all reasonable doubt, first, that 
the Gulf-stream really has its origin in the propulsive force of 
the trade-winds, and secondly, that the greatest disturbance of 
equilibrium which can be supposed to residt from the agencies 
invoked by Lieut. Maury would be utterly inadequate to 
generate and maintain either the Gulf-stream or any other 
sensible current" (§ 92). This being Dr. Carpenter's belief, it 
is somewhat singular that he should advance the case of the 
polar current passing under the Gulf-stream as evidence in 
favour of his theory ; for in reality he could hardly have 
selected a case more hostile to that theory. In short, it is 
evident that, if a polar current impelled by a force other than 
that of gravity can pass from the banks of Newfoundland to 
the Gulf of Mexico (a distance of some thousands of miles) 
under a current flowing in the opposite direction and, at the 
same time, so powerful as the GKilf-stream, it could pass much 
more easily under comparatively still water, or water flowing 
in the same direction as itself. And if this be so, then all our 
difficulties disappear, and we satisfactorily explain the presence 
of cold polar water at the bottom of inter-tropical seas 
without having recourse to the hypothesis advanced by Dr. 
Carpenter. 

But we have an example of an under current more inex- 
plicable on the gravitation hypothesis than even that of 
the polar current, viz., the warm under current of Davis 
Strait. 

There is a strong current flowing north from the Atlantic 
through Davis Strait into the Arctic Ocean imdemeath a sur- 
face current passing southwards in an opposite direction. Large 
icebergs have been seen to be carried northwards by this under 
oonent at the rate of four knots an hour against both the wind 
4iie Burfaoe current, ripping and tearing their way with 




THE GRAVITATION THEORY. 133 

terrific force throngli sorface ice of great thickness.* A current 
so powerful and rapid as this cannot, as Dr. Carpenter admits, 
be referred to difference of specific gravity. But even suppos- 
ing that it could, still difference of temperature between the 
equatorial and polar seas would not account for it; for the 
current in question flows in the wrong direction. Nor will it 
help the matter the least to adopt Maury's explanation, viz., 
that the warm under current from the south, in consequence of 
its greater saltness, is denser than the cold one from the polar 
regions. For if the water of the Atlantic, notwithstanding its 
higher temperature, is in consequence of its greater saltness so 
much denser than the polar water on the west of Greenland as 
to produce an under current of four knots an hour in the direction 
of the pole, then surely the same thing to a certain extent will 
hold true in reference to the ocean on the east side of Green- 
land. Thus instead of there being, as Dr. Carpenter supposes, 
an underflow of polar water south into the Atlantic in virtue of 
its greater density, there ought, on the contrary, to be a surface 
flow in consequence of its lesser density. 

The true explanation no doubt is, that the warm under 
current from the south and the cold upper-current from the 
north are both parts of one grand system of circulation produced 
by the winds, difference of specific gravity having no share 
whatever either in impelling the currents, or in determining 
which shall be the upper and which the lower. 

The wind in Baffin's Bay and Davis Strait blows nearly 
always in one direction, viz. from the north. The tendency of 
this is to produce a surface or upper current from the north 
down into the Atlantic, and to prevent or retard any surface 
current from the south. The warm current from the Atlantic, 
taking the path of least resistance, dips under the polar current 
and pursues its course as an under current. 

Mr. Clements Markham, in his " Threshold of the Unknown 
Region," is inclined to attribute the motion of the icebergs to 

• See "Physical Geography of the Soa/* chap, ix., new o<iition, and Dr. A. 
Mahry ** On 6cean-cuiTent»in the Circumpolar fiasin of the North Hemisphere.* 



134 CLIMATE AND TIME. 

tidal action or to counter under currents. That the motiou of 
the icebergs cannot reasonably be attributed to the tides is, I 
think, evident from the descriptions given both by Midshipman 
Oriffin and by Captain Duncan, who distinctly saw the icebergs 
moving at the rate of about four knots an hour against a sur&ce 
current flowing southwards. And Captain Duncan states that 
the bergs continued their course northwards for several days, 
till they ultimately disappeared. The probability is that this 
northward current is composed partly of Gulf-stream water and 
partly of that portion of polar water which is supposed to flow 
round Cape Farewell from the east coast of Greenland. This 
stream, composed of both warm and cold water, on reaching to 
about latitude 65° N., where it encounters the strong northerly 
winds, dips down under the polar current and continues its 
northward course as an under current. 

We have on the west of Spitzbergen, as has already been 
noticed, a similar example of a warm current from the south 
passing under a polar current. A portion of the Gulf-stream 
which passes round the west coast of Spitzbergen flows under 
an arctic current coming down from the north ; and it does so 
no doubt because it is here in the region of prevailing northerly 
winds, which favour the polar current but oppose the Gulf- 
stream. Again, we have a cold and rapid current sweep *ng 
round the east and south of Spitzbergen, a current of which 
Mr. Lamont asserts that he is positive he has seen it running 
at the rate of seven or eight miles an hour. This current, on 
meeting the Gulf-stream about the northern entrance to the 
German Ocean, dips down imder that stream and pursues its 
course southwards as an under current. 

Several other cases of under currents might be adduced which 
cannot be explained on the gravitation theory, and which must 
be referred to a system of oceanic circulation produced by the 
impulse of the wind ; but these will suffice to show that the 
assumption that the winds can produce only a mere surface drift 
is directly opposed to facts. And it will not do to affirm that a 
Gorrent which forms part of a general system of circulation 



THE GRAVITATION THEORY 135 

produced by the impulse of the winds cannot possibly be an 
under current ; for in the case referred to we have proof that 
the thing is not only possible but actually exists. This point, 
however, will be better understood after we have considered the 
evidence in favour of a general system of oceanic currents. 

Much of the difficulty experienced in comprehending how 
under currents can be produced by the wind, or how an impulse 
imparted to the surface of the ocean can ever be transmitted to 
the bottonl, appears to me to result, to a considerable extent at 
least, from a slight deception of the imagination. The thing 
which impresses us most forcibly in regard to the ocean is its 
profound depth, A mean depth of, say, three miles produces a 
striking impression ; but if we could represent to the mind the 
vast area of the ocean as correctly as we can its depth, skaliofv* 
ne;^ rather than depth would be the impression produced. If 
in crossing a meadow we found a sheet of water one hundred 
yards in diameter and only an inch in depth, we should not call 
that a deepy but a very shallow pool. The probability is that we 
should speak of it as simply a piece of ground covered with a 
thin layer of water. Yet such a thin layer of water would be 
a correct representation in miniature of the ocean; for the 
ocean in relation to its superficial area is as shallow as the pool 
of our illustration. In reference to such a pool or thin film of 
water, we have no difficulty in conceiving how a disturbance on 
its sur&ce would be transmitted to its bottom. In fact our 
difficulty is in conceiving how any disturbance extending over 
its entire surface should not extend to the bottom. Now if we 
coidd form as accurate a sensuous impression of the vast area of 
the ocean as we do of such a pool, all our difficulty in under- 
standing how the impidses of the wind acting on the vast area 
of the ocean should communicate motion down to its bottom 
would disappear. It is certainly true' that sudden commotions 
caused by storms do not generally extend to great depths. 
Neither will winds of short continuance produce a current 
extending far below the surface. But prevailing winds which 
oan produce such immense surface flow as that of the great 



1 3b CLIMATE AND TIME, 

equatorial currents of the globe and the Gulf-stream^ which 
follow definite directions, must communicate their motion to 
great depths, unless water be frictionless, a thing which it is 
not. Suppose the upper layer of the ocean to be forced on by 
the direct action of the winds with a constant velocity of, 
say, four miles an hour, the layer immediately below will be 
dragged along with a constant velocity somewhat less than four 
miles an hour. The layer immediately below this second layer 
will in turn be also dragged along with a constant velocity 
somewhat less than the one above it. The same will take place 
in regard to each succeeding layer, the constant velocity of 
each layer being somewhat less than the one immediately above 
it, and greater than the one below it. The question to be 
determined is, at what depth will all motion cease ? I presume 
that at present we have not sufficient data for properly 
determining this point. The depth will depend, other things 
being equal, upon the amount of molecular resistance oflFered 
by the water to motion — in other words, on the amount of the 
shearing-force of the one layer over the other. The feet, how- 
ever, that motion imparted to the surface will extend to great 
depths can be easily shown by direct experiment. If a constant 
motion be imparted to the surface of water, say, in a vessel, 
motion will ultimately be communicated to the bottom, no 
matter how wide or how deep the vessel may be. The same 
effect will take place whether the vessel be 5 feet deep or 500 
feet deep. 

The knoicn Condition of the Ocean inconsistent with Dr, Car- 
penter' 8 Hypothesis, — Dr. Carpenter says that he looks forward 
with great satisfaction to the results of the inquiries which are 
being prosecuted by the Circumnavigation Expedition, in the 
hope that the facts brought to light may establish his theory of 
a general oceanic circulation ; and he specifies certain of these 
facts which, if found to be correct, will establish his theory. It 
seems to me, however, that the facts to which he refers are just 
as explicable on the theory of under currents as on the theory 
of a general oceanic circulation. He begins by saying, " If the 



737^ GRAVITATION THEORY. 137 

TiewB I have propounded be correct, it may be expected that 
near the border of tbe great antarctic ice-barrier a temperature 
below 30^ will be met with (as it has been by Parry, Martens, 
and Weyprecht near Spitzbergen) at no great depth beneath 
the surface, and that instead of rising at still greater depths, 
the thermometer will fall to near the freezing-point of salt water " 
(§39). 

Dr. Carpenter can hardly claim this as evidence in favour of 
his theory ; for near the borders of the ice-barrier the water, as 
a matter of course, could not be expected to have a much higher 
temperature than the ice itself. And if the observations be 
made during summer months, the temperature of the water at 
the surface will no doubt be found to be higher than that of the 
bottom ; but if they be carried on during winter, the surface- 
temperature will doubtless be found to be as low as the bottom- 
temperature. These are results which do not depend upon any 
particular theory of oceanic circulation. 

"The bottom temperature of the North Pacific," he con- 
tinues, " will afford a crucial test of the truth of the doctrine. 
For since the sole communication of this vast oceanic area with 
the arctic basin is a strait so shallow as only to permit an 
inflow of warm surface water, its deep cold stratum must be 
entirely derived from the antarctic area ; and if its bottom 
temperature is not actually higher than that of the South 
Pacific, the glacial stratum ought to be found at a greater 
depth north of the equator than south of it " (§ 39). 

This may probably show that the water came from the ant- 
arctic regions, but cannot possibly prove that it came in the 
manner which he supposes. 

" In the North Atlantic, again, the comparative limitation of 
communication with the arctic area may be expected to prevent 
its bottom temperature from being reduced as low as that of 
the Southern Atlantic" (§39). Supposing the bottom tem- 
perature of the South Atlantic should be found to be lower 
than the bottom temperature of the North Atlantic, this 
fact will be just as consistent with the theory of under 



ijS CLIMATE AND TIME. 

oarrents as with his theory of a general movement of the 
ocean. 

I am also wholly unable to comprehend how he should 
imagine, because the bottom temperature of the South Atlantic 
happens to be lower, and the polar water to lie nearer to the 
surface in this ocean than in the North Atlantic, that therefore 
this proves the truth of his theory. This condition of matters 
is just as consistent, and even more so, as will be shown in 
Chapter XIII., with my theory as with his. When we consider 
the immense quantity of warm surface water which, as has been 
shown (Chapter V.), is being constantly transferred from the 
South into the North Atlantic, we readily understand how the 
polar water comes nearer to the surface in the former ocean than 
in the latter. Every pound of water, of course, passing &om the 
southern to the northern hemisphere must be compensated by 
an equal amount passing from the northern to the southern 
hemisphere. But nevertheless the warm water drained off the 
South Atlantic is not replaced directly by water from the north, 
but by that cold antarctic current, the existence of which is, 
unfortunately, too well known to navigators from the immense 
masses of icebergs which it brings along with it. In fact, the 
whole of the phenomena are just as easily explained upon the 
principle of under currents as upon Dr. Carpenter's theory. 
But we shall have to return to this point in Chapter XIII., when 
we come to discuss a class of facts which appear to be wholly 
irreconcilable with the gravitation theory. 

Indeed I fear that even although Dr. Carpenter's expecta- 
tions should eventually be realised in the results of the Cir- 
cumnavigation Expedition, yet the advocates of the wind 
theory will still remain unconverted. In fact the Director of 
this Expedition has already, on the wind theory, offered an 
explanation of nearly all the phenomena on which Dr. Car- 
penter relies ; * and the same has also been done by Dr. 
Petermann,t who, as is well known, is equally opposed to 

• *' Depths of the Sea/' Nature for July 28, 1870. 

t " Memoir on the Gulf-stream/' OeoffraphUche MittJmlungen^ vol. xvi. (1870) 



THE GRAVITATION THEORY. 139 

Dr. Carpenter's theory. Dr. Carpenter directs attention to the 
necessity of examining the broad and deep channel separating 
Iceland from Greenland. The observations which have already 
been made, however, show that nearly the entire channel is 
occupied, on the surface at least, by water flowing southward 
from the polar area — a direction the opposite of what it ought 
to be according to the gravitation theory. In fact the surface of 
one half of the entire area of the ocean, extending from Green- 
land to the North Cape, is moving in a direction the opposite of 
that which it ought to take according to the theory under 
review. The western half of this area is occupied by water 
which at the surface is flowing southwards ; while the eastern 
half, which has hitherto been regarded by almost everybody 
but Dr. Carpenter himself and Mr. Findlay as an extension of 
the Ghilf-stream, is moving polewards. The motion of the 
w^tem half must be attributed to the winds and not to gravity ; 
for it is moving in the wrong direction to be accounted for by 
the latter cause ; but had it been moving in the opposite 
direction, no doubt its motion would have been referred to 
gravitation. To this cause the motion of the eastern half, 
which is in the proper direction, is attributed ; * but why not 
assign this motion also to the impulse of the winds, more 
especially since the direction of the prevailing winds blowing 
over that area coincides with that of the water ? If the wind 
can produce the motion of the water in the western half, why 
may not it do the same in the eastern half? 

If there be such a difierence of density between equatorial 
and polar waters as to produce a general flow of the upper 
portion of the ocean poleward, how does it happen that one 
half of the water in the above area is moving in opposition to 
gravity ? How is it that in a wide open sea gravitation should 
act so powerfully in the one half of it and with so little effect 
in the other half ? There is probably little doubt that the ice- 
cold water of the western half extends from the surface down to 

• Dr. Carpenter " On the Gulf-stream/* rroceoJings of Royal Geographical 
Society for January 9, 1871, { 29. 



I40 CLIMATE AND TIME. 

the Ix/itom. And it ijb abo probable that the bottom wmttf u 
moTing southwards in the same direction as the sorfiioe water. 
The bottom water in such a case would be moTing in hannonj 
with the gravitation theory ; but woidd Dr. Carpenter on this 
account attribute its motion to g^vity ? Would he attribute 
the motion of the lower half to gravity and the upper half 
to the wind ? He could not in consistency with his theory 
attribute the motion of the upper half to gravity : for although 
the ico-cold water extended to the surface, this could not 
explain how gravity should move it southward instead of pole- 
wards, as according to theory it ought to move. He might 
affirm, if ho chose, that the surface water moves southwards 
bccauHO it is dragged forward by the bottom water ; but if this 
view bo hold, ho is not entitled to affirm, as he does, that the 
winds can only produce a mere surface drift. If the viscosity 
and niohjculur resistance of water be such that, when the lower 
strata of tlio ocean are impelled forward by gravity or by any 
other cause, the superincumbent strata extending to the surface 
arc perforce dragged after them, then, for the same reason, 
when tlio upper strata are impelled forward by the wind or any 
other cause, the underlying strata must also be dragged along 
after them. 

If the condition of the ocetm between Greenland and the 
north-western shore of Europe is irreconcilable with the gravi- 
tation tluM)ry, we ilnd the case even worse for that theory when 
wo dircK't our attention to the condition of the ocean on the 
southern hemisphere ; for according to the researches of Cap- 
tain Duperrey and others on the currents of the Southern 
Ocean, a very large portion of the area of that ocean is occupied 
by water moving on the surface more in a northward than a 
jH>lewanl direction. Keferring to the deep trough between the 
Shot hind and the Faroe Islands, called by him the "Lightning 
Channel,*' Dr. Carpenter says, "If my view be correct, a 
ourrt>ut-drag suspended in the upper strahmi ought to have a 
pt^rcoptiblo movement in the N.E. direction; whilst another, 
suspended in the hxcer stratum, should move S.W." (§ 40). 



THE GRAVITATION THEORY. 141 

Any one beliering in the north-eastern extension of the 
Gulf-stream and in the Spitzbergen polar under current, to 
which I have already referred, would not feel surprised to 
learn that the surface-strata have a perceptible north-eastward 
motion, and the bottom strata a perceptible south-westward 
motion. Korth-east and east of Iceland there is a general flow 
of cold polar water in a south-east direction towards the left 
edge of the Gulf-stream. This water, as Professor Mohn con- 
cludes, ** descends beneath the GKilf- stream and partially finds 
an outlet in the lower half of the Faroe-ShetLind channel/'* 

An Objection Considered. — In Nature^ vol. ix. p. 423, Dr. 
Carpenter has advanced the following objection to the foregoing 
theory of under currents : — " According to Mr. Croll's doctrine, 
the whole of that vast mass of water in the North Atlantic, 
averaging, say, 1,500 fathoms in thickness and 3,600 miles in 
breadth, the temperature of which (from 40° downwards), as 
ascertained by the Challenger soundings, clearly shows it to be 
mainly derived from a polar source, is nothing else than the 
reflux of the (hilf-stream. Now, even if we suppose that the 
whole of this stream, as it passes Sandy Hook, were to go on 
into the closed ajctic basin, it would only force out an equiva- 
lent body of water. And as, on comparing the sectional areas 
of the two, I find that of the Gulf-stream to be about 1 -900th 
that of the North Atlantic underflow ; and as it is admitted 
that a large part of the Gulf-stream returns into the Mid- 
Atlantic circidation, only a branch of it going on to the north- 
east, the extreme improbability (may I not say impossibility P) 
that so vast a mass of water can be put in motion by what is 
by comparison a mere rivulet (the north-east motion of which, 
as a distinct current, has not been traced eastward of 30° W. 
long.) seems still more obvious." 

In this objection three things are assumed : (1) that the 
mass of cold water 1,500 fathoms deep and 3,600 miles in 
breadth is in a state of motion towards the equator ; (2) that it 
cannot be the reflux of the Gulf- stream, because its sectional 

• Dr. Pelermann's Mittheihitigen ft>r 1872, p. 315 



i^i CLIMATE AND TIME. 

area is 900 times as great as that of the Gulf-stream ; (3) that 
the immense mass of water is, according to my views, set in 
motion by the Gulf-stream. 

As this objection hus an important bearing on the question 
under consideration, I shall consider these three assumptions 
separately and in their order : (1) That this immense mass of 
cold water came originally from the polar regions I, of course, 
admit, but that the whole is in a state of motion I certainly do 
not admit. There is no warrant whatever for any such assump- 
tion. According to Dr. Carpenter himself, the heating-power 
of the sun docs not extend to any great depth below the sur- 
face ; consequently there is nothing whatever to heat this mass 
but the heat coming through the earth's crust. But the amount 
of heat derived from this source is so trifling, that an under 
current from the arctic regions far less in volume than that of 
the GuK-stream would be quite sufficient to keep the mass at 
an ice-cold temperature. Taking the area of the North Atlantic 
between the equator and the Tropic of Cancer, including also 
the Caribbean Sea and the Gulf of Mexico, to be 7,700,000 
square miles, and the rate at which internal heat passes through 
the earth's surface to be that assigned by Sir William Thomson, 
we find that the total quantity of heat derived from the earth's 
crust by the above area is equal to about 88 X 10^^ foot-pounds per 
day. But this amount is equal to only l-894th that conveyed 
by the Gulf-stream, on the supposition that each pound of 
water carries 19,300 foot-pounds of heat. Consequently an 
under current from the polar regions of not more than l-35th the 
volume of the Gulf -stream would suffice to keep the entire mass 
of water of that area within 1° of what it would be were there 
no heat derived from the crust of the earth ; that is to say, 
were the water conveyed by the under current at 32^, internal 
heat would not maintain the mass of the ocean in the above 
area at more than 33^. The entire area of the North Atlantic 
fnun the equator to the arctic circle is somewhere about 
10,000,000 square miles. An under current of less than l-17th 
of the Gnlf-stream coming frt)m the arctic regions would 




THE GRAVITATION THEORY. 14.3 

therefore suffice to keep the entire North Atlautic basin filled 
with ice-cold water. In short, whatever theory we adopt 
regarding oceanic circulation, it follows equally as a necessary 
consequence that the entire mass of the ocean below the stratum 
heated by the sun's rays must consist of cold water. For ii 
cjld water be continually coming from the polar regions either 
in the form of under currents, or in the form of a general under- 
flow as Dr. Carpenter supposes, the entire under portion of the 
ocean must ultimately become occupied by cold water; for 
there is no source from which this influx of water can derive 
heat, save from the earth's crust. But the amount thus derived 
is 80 trifling as to produce no sensible effect. For example, a 
polar under current one half the size of the Oulf-stream would 
be sufficient to keep the entire water of the globe (below the 
stratum heated by the sun's rays) at an ice-cold temperature. 
Internal heat would not be sufficient under such circumstances 
to maintain the mass 1° Fahr. above the temperature it pos- 
sessed when it left the polar regions. 

It follows therefore that the presence of the immense mass of 
ice-cold water in the great depths of the ocean is completely 
accounted for by imder currents, and there is no necessity for 
supposing it to be all in a state of motion towards the equator. 
In fact, this very state of things, which the general oceanic cir- 
culation hypothesis was devised to explain, results as a necessary 
consequence of polar under currents. Unless these were entirely 
stopped it is physically impossible that the ocean could be in 
any other condition. 

But suppose that this immense mass of cold water occupying 
the great depths of the ocean were, as Dr. Carpenter assumes it 
to be, in a state of constant motion towards the equator, and 
that its sectional area were 900 times that of the Gulf-stream, 
it would not therefore follow that the quantity of water passing 
through this large sectional area must be greater than that 
flowing through a sectional area of the Gulf-stream ; for the 
quantity of water flowing through this large sectional area 
depends entirely on the rate of motion. 



«i4 



CLIMATE AND TIME, 



I am wholly unable to understand how it could bo supposed 
that this underflow, according to mj yiew, is set in motion by 
the Gulf-stream, seeing that I have shown that the return 
under current is as much due to the impulse of the wind as the 
Gulf-stream itself. 

Dr. Carpenter lays considerable stress on the important fSu^ 
established by the Challenger expedition, that the great depths 
of the sea in equatorial regions are occupied by ice-cold water, 
while the portion heated by the sun's rays is simply a thin 
stratum at the surface. It seems to me that it would be difficult 
to find a fact more hostile to his theory than this. Were it not 
for this upper stratum of heated water there would be no differ- 
ence between the equatorial and polar columns, and conse* 
quently nothing to produce motion. But the thinner this 
stratum is the less is the difference, and the less there is to 
produce motion. 



CHAPTER IX. 

EXAMINATION OF THK GRAVITATION THEORY OF OCEANIC CIR- 
CULATION. — ^THE MECHANICS OF DR. CARPENTER's THEORY. 

Bzpenmental IHoBtration of the Theory.— -The Force exerted by Gravity.— 
Work performed by Gravity. — Circulation not by Convection. — Circulation 
depondB on Difierence in iJensity of the Equat(>rial and Polar Colonins. — 
Absolute Amount of Work which can be performed by Gravity. — How 
Underflow is produced. — How Vertical Descent at the Poles and Ascent at 
the Equator is produced. — The Gibraltar Current. — Mistake in Mechanics 
eonceming it. — The Baltic Current. 

&perim€nt to illustrate Theonj. — In support of the theory of 
a general movement of water between equatorial and polar 
regions, Dr. Carpenter adduces the authority of Humboldt and 
of Prof, Buff.* I have been unable to find anything in the 
writings of either from which it can be inferred that they have 
given this matter special consideration. Humboldt merely 
alludes to the theory, and that in the most casual manner ; and 
that Prof. Buff has not carefully investigated the subject is 
apparent from the very illustration quoted by Dr. Carpenter 
from the " Physics of the Earth." ** The water of the ocean 
at great depths," says Prof. Buff, " has a temperature, even 
under the equator, nearly approaching to the freezing-point. 
This low temperature cannot depend on any influence of the sea- 
bottom The fact, however, is explained by a continual 

current of cold water flowing from the polar regions towards 
the equator. The following well-known experiment clearly 
iilostrates the manner of this movement. A glass vessel is to 
be filled with water with which some powder has been mixed, 
and is then to be heated at bottom. It will soon be seen, from 

• Proceedings of the Royal Society, vol. xvii., p. 187, xviii., p. 463. 



146 CLIMATE AND TIME. 

the motion of the particles of powder, that currents are set up 
in opposite directions through the water. Warm water rises 
from the bottom up through the middle of the vessel, and spreads 
over the surface, while the colder and therefore heavier liquid 
falls down at the sides of the glass." 

This illustration is evidently intended to show not merely the 
form and direction of the great system of oceanic circulation, 
but also the mode in which the circulation is induced by heat 
It is no doubt true that if we apply heat (say that of a spirit- 
lamp) to the bottom of a vessel filled with water, the water at 
the bottom of the vessel will become heated and rise to the 
surface ; and if the heat be continued an ascending current of 
warm water will be generated ; and this, of course, will give 
rise to a compensating under current of colder water from all 
sides. In like manner it is also true that, if heat were applied 
to the bottom of the ocean in equatorial regions, an ascending 
current of hot water would be also generated, giving rise to an 
under current of cold water from the polar regions. But aU 
this is the diametrically opposite of what actually takes place in 
nature. The heat is not applied to the bottom of the ocean, so 
as to make the water there lighter than the water at the sur- 
face, and thus to generate an ascending current ; but the heat 
is applied to the surface of the ocean, and the efiect of this is to 
prevent an ascending current rather than to produce one, for it 
tends to keep the water at the surface lighter than the water at 
the bottom. In order to show how the heat of the sun pro- 
duces currents in the occun, Prof. Bufi" should have applied the 
heat, not to the bottom of his vessel, but to the upper surface 
of the water. But this is not all, the form of the vessel has 
something to do with the matter. The wider we make the vessel 
in proportion to its depth, the more difficult it is to produce 
currents by means of heat. But in order to represent what 
takes place in nature, we ought to have the same proportion 
between the depth and the superficial area of the wat^r in our 
vessel as there is between the depth and the superficial area of 
the sea. The mean depth of the sea may be taken roughly to 



THE GRA VITA TION THEORY. 1 47 

be about three mllee.* The distance between pole and pole we 
shall take in round numbers to be 12,000 miles. The sun may 
therefore be regarded as shining upon a circular sea 12,000 
miles in diameter and three miles deep. The depth of the sea 
to its diameter is therefore as 1 to 4,000. Suppose, now, that 
in our experiment we make the depth of our vessel one inch, we 
shall require to make its diameter 4,000 inches, or 333 feet, 
say, in round numbers, 100 yards in diameter. Let us, then,* 
take a pool of water 100 yards in diameter, and one inch deep. 
Suppose the water to be at 32°. Apply heat to the upper sur- 
face of the pool, so as to raise the temperature of the surface of 
the water to 80° at the centre of the pool, the temperature 
diminishing towards the edge, where it is at 32°. It is found 
that at a depth of two miles the temperature of the water at 
the equator is about as low as that of the poles. We must 
therefore suppose the water at the centre of our pool to diminish 
in temperature from the surface downwards, so that at a depth 
of half an inch the water is at 32°. We have in this case a 
thin layer of warm water half an inch thick at the centre, and 
gradually thinning off to nothing at the edge of the pool. The 
lightest water, be it observed, is at tho surface, so that an 
ascending or a descending current is impossible. The only 
way whereby the heat applied can have any tendency to pro- 
duce motion is this : — The heating of the water expands it, 
consequently the surface of the pool must stand at a little 
higher level at its centre than at its edge, where no expansion 
takes place ; and therefore, in order to restore the level of the 
pool, the water at the centre will tend to flow towards the 
sides. But what is the amount of this tendency ? Its amount 
will depend upon the amount of slope, but the slope in the case 
under consideration amounts to only 1 in 7,340,000. 

Dr, Carpenter^ 8 Experiment, — In order to obviate the ob- 
jection to Professor Huff's experiment Dr. Carpenter has devised 

• The average depth of the Pacific Ocy^nn, as found by the soundiiips of 
Captain Belknap, of tho U.S. steamer Tmcarora^ made during January and 
February, 1874, is about 2,400 fathoms. The depth of the Atlantic is somewhat 
leas. 



148 CLIMATE AND TIME. 

snother mode. But I presume his experiment was intended 
rather to illustrate the way iu which the circulation of the 
ocean, according to his theory, takes place, than to prove that 
it actually does take place. At any rate, all that can be claimed 
for the experiment is the proof that water will circulate in con- 
sequence of difi'erence of specific gravity resulting &om differ- 
ence of temperature. But this does not require proof, for no 
^physicist denies it. The point which requires to be proved is 
this. Is the difference of specific gravity which exists in the 
ocean sufficient to produce the supposed circulation ? Now his 
mode of experimenting will not prove this, imless he makes his 
experiment agree with the conditions already stated. 

But I decidedly object to the water being heated in the way 
in which it has been done by him in his experiment before the 
Royal Geographical Society ; for I feel somewhat confident that 
in this experiment the circulation resulted not from difference 
of specific gravity, as was supposed, but rather from the way in 
which the heat was applied. In that experiment the one half 
of a thick metallic plate was placed in contact with the upper 
surface of the water at one end of the trough ; the other half, 
projecting over the end of the trough, was heated by means of 
a spirit-lamp. It is perfectly obvious that though the tempera- 
ture of the great mass of the water under the plate might not 
be raised over 80° or so, yet the molecules in contact with the 
metal would have a very high temperature. These molecules, 
in consequence of their expansion, would be unable to sink into 
the cooler and denser water underneath, and thus escape the 
heat which was being constantly commimicated to them from 
the heated plate. But escape they must, or their temperature 
would continue to rise imtil they would ultimately burst into 
vapour. They cannot ascend, neither can they descend : they 
therefore must be expelled by the heat from the plate in a hori- 
zontal direction. The next layer of molecules from beneath would 
take their place and would be expelled in a similar manner, 
and this process would continue so long as the heat was applied 
^^^e plate. A circulation would thus be established by the 



THE GRAVITATION THEORY. 149 

direct expansiTe force of yapour, and not in any way due to 
difference of specific gravity, as Dr. Carpenter supposes. 

But supposing the heated bar to be replaced by a piece of 
ice, circulation would no doubt take place ; but this proves 
nothing more than that difference of density will produce circu- 
lation, which is what no one calls in question. 

The case referred to by Dr. Carpenter of the heating apparatus 
in London University is also unsatisfactory. The water leave/ 
the boiler at 120° and returns to it at 80°. The difference of 
specific gravity between the water leaving the boiler and the 
water returning to it is supposed to produce the circulation. 
It seems to me that this difference of specific gravity has 
nothing whatever to do with the matter. The cause of the 
circulation must be sought for in the boiler itseK, and not in 
the pipes. The heat is applied to the bottom of the boiler, not 
to the top. What is the temperature of the molecules in 
contact with the bottom of the boiler directly over the fire, is a 
question which must be considered before we can arrive at a 
just determination of the causes which produce circulation in 
the pipes of a heating apparatus such as that to which Dr. 
Carpenter refers. But, in addition to this, as the heat is 
applied to the bottom of the boiler and not to the top, con- 
vection comes into play, a cause which, as we shall find, does 
not come into play in the theory of oceanic circulation at 
present under our consideration. 

The Force exerted by Oravity. — Dr. Carpenter speaks of his 
doctrine of a general oceanic circulation sustained by difference 
of temperature alone, " as one of which physical geographers 
could not recognise the importance, so long as thoy remained 
under the dominant idea that the temperature of the deep sea 
is everywhere 39°." And he affirms that " until it is clearly 
apprehended that sea-water becomes more and more dense as 
its temperature is reduced, the immense motive power of polar 
cold cannot be understood." But in chap. vii. and also in the 
PhiL Mag. for October, 1870 and 1871, I proved that if we 
take 39° as the temperature of maximum density the force 



ISO CLIMATE AND TIME. 

exerted by gravity tending to produce circulation is just as 
great as when we take 82^. The reason for this is that when 
we take 82° as the temperature of maximum density, although 
we have, it is true, a greater elevation of the ocean above the 
place of maximum density, yet this latter occurs at the poles ; 
while on the other hand, when we take 39°, the difference of 
level is less — the place not being at the poles but in about 
lat. 5C°. Now the shorter slope from the equator to lat. 66° is 
as steep as the larger one from the equator to the poles, and 
consequently gravity exerts as much force in the production of 
motion in the one case as in the other. Sir John Herschel, 
taking 89° as the temperature of maximum density, estimated 
the slope at l-82nd of an inch per mile, whereas we, taking 
82° as the actual temperature of maximum density of the polar 
seas and calcidating from modem data, find that the slope is 
not one-half that amount, and that the force of gravity tending 
to produce circulation is much less than Herschel concluded it 
to be. The reason, therefore, why physical geographers did 
not adopt the theory that oceanic circulation is the result of 
difference of temperature could not possibly be the one assigned 
by Dr. Carpenter, viz., that they had under-estimated the force 
of gravity by taking 89° instead of 82^ as the temperature of 
maximum density. 

The Work performed hy Gravity, — But in order clearly to 
understand this point, it will be better to treat the matter 
according to the tliird method, and consider not the mevG force 
of gravity impelling the waters, but the amount of Kork which 
gravitation is capable of performing. 

Let us then assume the correctness of mv estimate, that the 
height of the surface of the ocean at the equator above that at 
the poles is 4 feet 6 inches, for in representing the mode in 
which difference of specitic gravity produces circulation it is of 
no importance what we may fix upon as the amount of the 
slope. In order, therefore, to avoid fractions of a foot, I shall 
take the slope at 4 feet instead of 44 feet, which it actually is. 
A poond of water in flowing down this slope from the equator to 



THE GRAVITATION THEORY. 151 

either of the poles will perform 4 foot-pounds of work; or. 
more properly speaking, gravitation will. I^ow it is evident 
thai when this pound of water has reached the pole, it is at the 
bottom of the slope, and consequently cannot descend further. 
Ghravity, therefore, cannot perform any more work upon it ; as it 
can only do so while the thing acted upon continues to descend 
—that is, moves under the force exerted. But the water will 
not move under the influence of gravity unless it move down- 
ward ; it being in this direction only that gravity acts on the 
water. " But," says Dr. Carpenter, " the effect of surface-cold 
upon the water of the polar basin will be to reduce the tempera- 
ture of its whole mass below the freezing-point of fresh water, 
the surface stratum sinking as it is cooled in virtue of its 
diminished bulk and increased density, and being replaced by 
water not yet cooled to the same degree."* By the cooling of 
the whole mass of polar water by cold and the heating of the 
water at the equator by the sun's rays the polar column of 
water, as we have seen, is rendered denser than the equatorial 
one, and in order that the two may balance each other, the 
polar column is necessarily shorter than the equatorial by 
4 feet ; and thus it is that the slope of 4 feet is formed. It is 
perfectly true that the water which leaves the equator warm 
and light, becomes by the time it reaches the pole cold and 
dense. But unless it be denser than the underlying polar water 
it will not sink do^Ti through it.f We are not told, however, 
why it should be colder than the whole mass underneath, which, 
according to Dr. Carpenter, is cooled by polar cold. But that 
he does suppose it to sink to the bottom in consequence of 
its contraction by cold would appear from the following 
quotation : — 

" Until it is clearly apprehended that sea-water becomes 

• Proceedings of Royal Geographical Society, vol. xv., { 22. 

t It is a well-eutablished fact that in polar regions the temperature of the sea 
decreases from the surface downwards; and the German Polar Expedition found 
that the water in very high latitudes is actually less dense at the surface than at 
considerable depths, thus proving that the surfisice-water could not sink in conse- 
quonce of its greater density. 

8 



152 CLIMATE AND TIME. 

more and more dense as its temperature is reduced, and that 
it consequently continues to sink until it freezes, the immense 
motor power of polar cold cannot be apprehended. But when 
this has been clearly recognised, it is seen that the application 
of cold at the surface is precisely equivalent as a moving power 
to that application of heat at the bottom by which the circulation 
of water is sustained in every heating apparatus that makes use 
of it " (§ 25). 

The application of cold at the surface is thus held to be 
equivalent as a motor power to the application of heat at the 
bottom. But heat applied to the bottom of a vessel produces 
circidation by convection. It makes the molecules at the 
bottom expand, and they, in consequence of buoyancy, rise 
through the water in the vessel. Consequently if the action of 
cold at the surface in polar regions is equivalent to that of 
heat, the cold must contract the molecules at the surface and 
make them sink through the mass of polar water beneath. But 
assuming this to be the meaning in the passage just quoted, 
how much colder is the surface water than the water beneath P 
Let us suppose the difference to be one degree. How much 
work, then, will gravity perform upon this one pound of water 
which is one degree colder than the mass beneath supposed to 
be at 32^ ? The force with which the pound of water will sink 
will not be proportional to its weight, but to the difference of 
weight between it and a similar bulk of the water through 
which it sinks. The difference between the weight of a pound 
of water at 31° and an equal volume of water at 32° is 
l-29,000th of a pound. Xow this pound of water in sinking to 
a depth of 10,000 feet, which is about the depth at which a 
polar temperature is found at the equator, would perform only 
one- third of a foot-pound of work. And supposing it were 
three degrees colder than the water beneath, it would in 
sinking perform only one foot-pound. This would give us 
only 4 + 1 = 5 foot-pounds as the total amount that could be 
performed by gravifcition on the pound of water from the time 
that it left the equator till it returned to the point from whiclj 




THE GRAVITATION THEORY. 153 

it started. The amount of work performed in descending the 
slope from the equator to the pole and in sinking to a depth of 
10,000 feet or so through the polar water assumed to be warmer 
than the surface water, comprehends the total amount of work 
that gravitation can possibly perform ; so that the amount of 
force gained by such a supposition over and above that derived 
from the slope is trifling. 

It would appear, however, that this is not what is meant 
after all. What Dr. Carpenter apparently means is this : when 
a quantity of water, say a layer one foot thick, flows down 
from the equator to the pole, the polar column becomes then 
heavier than the equatorial by the weight of this additional 
layer. A layer of water equal in quantity is therefore pressed 
away from the bottom of the column and flows off in the 
direction of the equator as an under current, the polar column 
at the same time sinking down one foot until equilibrium of the 
polar and equatorial columns is restored. Another foot of 
water now flows down upon the polar column and another foot 
of water is displaced from below, causing, of course, the column 
to descend an additional foot. The same process being con- 
tinually repeated, a constant downward motion of the polar 
column is the result. Or, perhaps, to express the matter 
more accurately, owing to the constant flow of water from the 
equatorial regions down the slope, the weight of the polar 
column is kept always in excess of that of the equatorial ; 
therefore the polar column in the effort to restore equilibrium 
is kept in a constant state of descent. Hence he terms it a 
"vertical" circulation. The following will show Dr. Car- 
penter's theory in his own words : — 

" The action of cold on the surface water of ejch polar area 
will be exerted as follows : — 

" (a) In diminishing the height of the polar column as com- 
pared with that of the equatorial, so that a lowering of its Uvel 
is produced, which can only be made good by a surface-flow 
from the latter towards the former. 

" (6) In producing an excess in the downward pressure of the 



154 CLIMATE AND TIME. 

column when this inflow has restored its level, in virtue of the 
increase of specific gravity it has gained by its reduction in 
volume ; whereby a portion of its heavy bottom- water is dis- 
placed laterally, causing a further reduction of level, which 
draws in a further supply of the warmer and lighter water 
flowing towards its surface. 

" (c) In imparting a downward movement to each new sur&ce- 
stratum as its temperature undergoes reduction ; so that the 
entire column may be said to be in a state of constant descent, 
like that which exists in the water of a tall jar when an opening 
is made at its bottom, and the water which flows away through 
it is replaced by an equivalent supply poured into the top of 
the jar" (§23). 

But if this be his theory, as it evidently is, then the 4 foot- 
pounds (the amount of work performed by the descent of the 
water down the slope) comprehends all the work that gravi- 
tation can perform on a pound of water in making a complete 
circuit from the equator to the polo and from the pole back to 
the equator. 

This, I trust, will be evident from the following considera- 
tions. When a pound of water has flowed down from the 
equator to the pole, it has descended 4 feet, and is then at the 
foot of the slope. Gravity lias therefore no more power to pull 
it down to a lower level. It will not sink through the polar 
water, for it is not denser than the water beneath on which it 
rests. But it may be replied that although it will not sink 
through the polar water, it has nevertheless made the polar 
column heavier than the equatorial, and this excess of pressure 
forces a pound of water out from beneath and allows the column 
to descend. Suppose it may be argued that a quantity of water 
flows down from the equator, so as to raise the level of the 
polar water by, say, one foot. The polar column will now be 
rendered heavier than the equatorial by the weight of one foot 
of water. The pressure of the one foot will thus force a 
quantity of water laterally from the bottom and cause the 
entire column to descend till the level of equilibrium is re- 



THE GRAVITATION THEORY. 



>5S 



•tored. In other words, the polar column will sink one foot. 
Now in the einking of this colunin work is performed by 
gravity. A certain amount of work is performed by gravity 
in causing the water to flow down the slope from the equator 
to the pole, and, in addition to this, a certain amoimt is per- 
formed by gravity in the vertical descent of the column. 

I freely admit this to be sound reasoning, and admit that so 
much is due to the slope and so much to the vertical descent of 
the water. But here we come to the most important point, 
viz., is there the fiill slope of 4 feet and an additional vertical 
movement? Dr. Carpenter seems to conclude that there is, 
and that this vertical force is something in addition to the force 
which I derive from the slope. And here, I venture to think, 
is a radical error into which he has fallen in regard to the 
whole matter. Let it be observed that, when water circulates 
from difference of specific gravity, this vertical movement is 
just as real a part of the process as the flow down the slope ; 
but the point which I maintain is that there is no additional 
power derived from this vertical movement over and above what is 
derived from the full slope — or, in other words, that this primum 
mobile, which he says I have overlooked, has in reality no 
existence. 

Perhaps the following diagram will help to make the point 

BtQl clearer : — 

Fig. 1. 




Let P (fig. 1) be the surface of the ocean at the pole, and 
E the surface at the equator ; P O a column of water at the 
polo, and E Q a column at the equator. The two columns are 



J56 CLIMATE AND TIME. 

of equal weight, and balance each other ; bnt as the polar water 
v^ colder, and consequently denser than the equatorial, the 
polar column is shorter than the equatorial, the difference in 
the lengt.h of the two columns being 4 feet. The surface of the 
ocoan at the equator E is 4 feet higher than the surface of the 
ocean at the pole P ; there is therefore a slope of 4 feet from E 
to P. Tlio molecules of water at E tend to flow down this 
slojH) towards P. The amount of work performed by gravity 
in the descent of a pound of water down this slope from E to 
P is therefore 4 foot-pounds. 

iJut of course there can be no permanent circulation while 
the full slope remains. In order to circulation the polar 
column must bo heavier than the equatorial. But any addition 
to tlio w(u^ht of \\\Q polar column is at the expense of the slope. 
In proportion ns the weight of the polar column increases the 
less b(HH)moH the slope. This, however, makes no difference in 
tho amount of work performed by gravity. 

Sup|)oso now that water has flowed down till an addition of 
one foot of water is made to the polar column, and the 
difforonoo of level, of course, diminished by one foot. The 
nurfuoo of tlio oo«\in in this case will now be represented by 
Iho dot toil lino P' K, and the slope reduced from 4 feet to 3 feet. 
Lot us thou suppose a pound of water to leave E and flow 
down to P' ; 3 toot-pounds will be the amount of work per- 
ft»ruuHl. TI\o polar column boinp^ now too heavy by the extent 
Of tho mass ot* wator P'P one ft>ot thick, its extra pressure 
oausos a mass of wator inpial to P' P to flow off laterally from 
tho K^ttom of tho colunni. Tho column therefore sinks down 
ono fivt till P* n\u hos P. >\>w tho p^nmd of wator in this 
vortical dcsoout fn^m P' to P has ono fcKn-pi^^und of work per- 
fv>rnu\l vn\ \t l\v cravity : this adiit\l to the l^ fwt -pounds derived 
iWm tho »lo}H\ civcs a total of 4 tlvt-jxm-^ds in passing from E 
to P' «:ul thou trv^m P* to 1\ This is tho same amount of work 
ih*! WK^uld haw Kvn p^Tfonut>d had it detsct?ndod dirvctly from 
Kl^> 1\ lu UkK> maamr it can bo prv vcd that 4 toot-poonds ia 
IM MKmm \^f wwk jy rtivTOod in tho d^^vn: of ovorv pound of 



THE GRAVITATION THEORY. 157 

irater of tHe mass P' P. The first poxind which left E flowed 
down the alope directly to P, and performed 4 foot-pounds of 
work. The last pound flowed down the slope E P^, and per- 
fitrmed only 3 foot-pounds ; but in descending &om P^ to P it 
performed the other one foot-pound. A pound leaving at a 
period exactly intermediate between the two flowed down 3^ 
feet of slope and descended vertically half a foot. Whatever 
path a pound of water might take, by the time that it reached 
P, 4 foot-pounds of work would be performed. But no further 
work can be performed after it reaches P. 

But some will ask, in regard to the vertical movement, is it 
only in the descent of the water from P' to P that work is 
performed P Water cannot descend from P' to P, it will be 
urged, unless the entire column P O underneath descend also. 
But the column P O descends by means of gravity. Why, then, 
it will be asked, is not the descent of the column a motive 
power as real as the descent of the mass of water P' P ? 

That neither force nor energy can be derived from the mere 
descent of the polar colunm P O is demonstrable thus: — The 
reason why the colimm P O descends is because, in consequence 
of the mass of water P' P resting on it, its weight is in excess 
of the equatorial column £ Q. But the force with which the 
column descends is equal, not to the weight of the column, but 
to the weight of the mass P' P ; consequently as much work 
would be performed by gravity in the descent of the mass P' P 
(the one foot of water) alone as in the descent of the entire 
column P' O, 10,000 feet in height. Suppose a ton weight is 
placed in each scale of a balance : the two scales balance each 
other. Place a pound weight in one of the scales along with 
the ton weight and the scale will descend. But it descends, 
not with the pressure of a ton and a pound, but with the pres- 
sure of the pound weight only. In the descent of the scale, 
say, one foot, gravity can perform only one foot-pound of work. 
In like manner, in the descent of the polar column, the only 
work available is the work of the mass P' P laid on the top of 
the column. But it must be observed that in the descent ol 



158 CLIMATE AND TIME. 

the column from P' to P, a distance of one foot, each pound of 
water of the mass P' P does not perform one foot-pound of 
work ; for the moment that a molecule of water reaches P, 
it then ceases to perform further work. The molecules at the 
surface P' descend one foot before reaching P ; the moleculefl 
midway between P' and P descend only half a foot before reach- 
ing P, and the molecules at the bottom of the mass are already 
at P, and therefore cannot perform any work. The mean dis- 
tance through which the entire mass performs work is therefore 
half a foot. One foot-pound per pound of water represents in 
this case the amount of work derived from the vertical move- 
ment. 

That such is the case is further evident from the following 
considerations. Before the polar column begins to descend, it 
is heavier than the equatorial by the weight of one foot of 
water ; but when the column has descended half a foot, the 
polar column is heavier than the equatorial by the weight of 
only half a foot of water; and, as the column continues to 
descend, the force with which it descends continues to diminish, 
and when it has sunk to P the force is zero. Consequently the 
mean pressure or weight with which the one foot of water P' P 
descended was equal to that of a layer of half a foot of water ; 
in other words, each pound of water, taking the mass as a 
whole, descended with the pressure or weight of half a pound. But 
a half pound descending one foot performs half a foot-pound ; 
60 that whether we consider the full pressure acting through the 
mean distance, or the mean pressure acting through the full dis- 
tance, we get the same result, viz. a half foot-pound as the work 
of vertical descent. 

Now it will be found, as we shall presently see, that if we 
calculate the mean amount of work performed in descending 
the slope from the equator to the pole, 3 J foot-pounds per 
pound of water is the amount. The water at the bottom of the 
mass P P' moved, of course, down the full slope E P 4 feet. 
The water at the top of the mass which descended from E to P' 
descended a slope of only 3 feet. The mean descent of the 



^^i>_ 



THE GRAVITATION THEORY. 159 

wHole mass is therefore 3^ feet. And this gives 3^ foot-pounds 
as the mean amount of work per pound of water in descending 
the slope; this, added to the half foot-pound deriyed from 
vertical descent, gives 4 foot-pounds us the total amount of 
work per pound of the mass. 

I have in the above reasoning supposed one foot of water 
accumulated on the polar column before any vertical descent 
takes place. It is needless to remark that the same conclusion 
would have been arrived at, viz., that the total amount of work 
performed is 4 foot-pounds per pound of water, supposing we 
had considered 2 feet, or 3 feet, or even 4 feet of water to 
have accumulated on the polar column before vertical motion 
took place. 

I have also, in agreement with Dr. Carpenter's mode of repre- 
senting the operation, been considering the two effects, viz., the 
flowing of the water down the slope and the vertical descent of 
the polar column as taking place alternately. In nature, how- 
ever, the two effects take place simultaneously ; but it is need- 
less to add that the amount of work performed would be the same 
whether the effects took place alternately or simultaneously. 

I have also represented the level of the ocean at the equator 
as remaining permanent while the alterations of level were 
taking place at the pole. But in representing the operation as 
it woidd actually take place in nature, we should consider the 
equatorial column to be lowered as the polar one is being raised. 
"We should, for example, consider the one foot of water P' P 
put upon the polar column as so much taken off the equatorial 
column. But in viewing the problem thus we arrive at exactly 
the same results as before. 

Let P (Fig. 2), as in Fig. 1, be the surface of the ooean at the 
pole, and E the surface at the equator, there being a slope of 
4 feet from E to P. Suppose now a quantity of water, E E', 
say, one foot thick, to flow from off the equatorial regions down 
upon the polar. It will thus lower the level of the equatorial 
column by one foot, and raise the level of the polar column by 
ihe same amount. I may, however, observe that the one foot 



1 60 



CL1MA7E AND TIME. 



of water in passing from E to P would Have its temperattura 
reduced from 80° to 32° and this would produce a slight con- 
Fig. 2. 




traction. But as the weight of the mass would not be affected, 
in order to simplify our reasoning we may leave this contraction 
out of consideration. Any one can easily satisfy himself that 
the assumption that E E' is equal to P' P does not in any 
way affect the question at issue — the only effect of the contrac- 
tion being to increase by an infinitesimal amount the work done 
in descending the slope, and to diminish by an equally infinites- 
imal amount the work done in the vertical descent. If, for 
example, 3 foot-pounds represent the amount of work performed 
in descending the slope, and one foot-pound the amount per- 
formed in the vertical descent, on the supposition that E' E does 
not contract in passing to the pole, then 3*0024 foot-poimds 
will represent the work of the slope, and 0*9976 foot-pounds the 
work of vertical descent when allowance is made for the con- 
traction. But the total amount of work performed is the same 
in both cases. Consequently, to simplify our reasoning, we 
may be allowed to assume P' P to be equal to E E'. 

The slope E P being 4 feet, the slope E' P' is consequently 
2 feet ; the mean slope for the entire mass is therefore 3 feet. 
The mean amount of work performed by the descent of the 
mass will of course be 3 foot-pounds per pound of water. The 
amount of work performed by the vertical descent of P'P 
ought therefore to be one foot-pound per pound. That this is 
the amount will be evident thus : — The transference of the one 



THE GRAVITATION THEORY. i6i 

loot of water from the equatorial column to the polar disturbs 
the equilibrium by making the equatorial column too light by 
one foot of water and the polar colunm too heavy by the same 
amount of water. The polar column will therefore tend to 
sink, and the equatorial to rise till equilibrium is restored. 
The difference of weight of the two columns being equal to 
2 feet of water, the polar column will begin to desceud with a 
pressure of 2 feet of water ; and the equatorial column will 
begin to rise with an equal amount of pressure. When the 
polar column has descended half a foot the equatorial column 
will have risen half a foot. The pressure of the descending 
polar column will now be reduced to one foot of water. And 
when the polar column has descended another foot, P' will 
have reached P, and E' will have reached £ ; the two columns 
will then be in equilibrium. It therefore follows that the 
mean pressure with which the polar column descended the one 
foot was equal to the pressure of one foot of water. Con- 
sequently the mean amount of work performed by the descent 
of the mass was equal to one foot-pound per pound of water ; 
thisy added to the 3 foot-pounds derived from the slope, gives a 
total of 4 foot-pounds. 

In whatever way we view the question, we are led to the 
conclusion that if 4 feet represent the amount of slope between 
the equatorial and polar columns when the two are in equi- 
librium, then 4 foot-pounds is the total amount of work that 
gravity can perform upon a pound of water in overcoming 
the resistance to motion in its passage from the equator to the 
pole down the slope, and then in its vertical descent to the 
bottom of the ocean. 

But it will be replied, not only does the one foot of water 
P'P descend, but the entire column P 0, 10,000 feet in length, 
descends also. What, then, it will be asked, becomes of the 
force which gravity exerts in the descent of this column P We 
shall shortly see that this force is entirely applied in work 
against gravity in other parts of the circuit ; so that not a 
single foot-poimd of this force goes to overcome cohesion. 



i62 CLIMA TE AND TIME. 

friction, and other resistances ; it is all spent in counteracting 
the efforts which gravity exerts to stop the current in another 
part of the circuit. 

I shall now consider the next part of the movement, viz., the 
under or return current from the bottom of the polar to the 
bottom of the equatorial column. What produces this current P 
It is needless to say that it cannot be caused directly by 
gravity. Gravitation cannot directly draw any body hori- 
zontally along the earth's surface. The water that forms this 
current is pressed out laterally by the weight of the polar 
column, and flows, or rather is pushed, towards the equator to 
supply the vacancy caused by the ascent of the equatorial 
column. There is a constant flow of water from the equator to 
the poles along the surface, and this draining of the water from 
the equator is supplied by the imder or return current from the 
poles. But the only power which can impel the water from 
the bottom of the polar column to the bottom of the equatorial 
column is the pressure of the polar column. But whence does 
the polar column derive its pressure P It can only press to the 
extent that its weight exceeds that of the equatorial column. 
That which exerts the pressure is therefore the mass of water 
which has flowed down the slope from the equator upon the 
polar column. It is in this case the vertical movement that 
causes this under current. The energy which produces this 
current must consequently be derived from the 4 foot-pounds 
resulting from the slope ; for the energy of the vertical move- 
ment, as has already been proved, is derived from this source ; 
or, in other words, whatever power this vertical movement may 
exert is so much deducted from the 4 foot-pounds derived from 
the full slope. 

Let us now consider the fourth and last movement, viz., the 
ascent of the imder current to the surface of the ocean at the 
equator. When this cold under current reaches the equatorial 
regions, it ascends to the surface to the point whence it origin- 
ally started on its circuit. What, then, lifts the water from 
the bottom of the equatorial column to its top P This cannot 



THE GRAVITATION THEORY. ibj 

bt. done directly, either by heat or by gravity. When heat, 
for example, is applied to the bottom of a vessel, the heated 
water at the bottom expands and, becoming lighter than the 
water above, rises through it to the surface ; but if the heat be 
applied to the surface of the water instead of to the bottom, the 
heat will not produce an ascending current. It will tend rather 
to prevent such a current than to produce one — the reason 
being that each successive layer of water will, on account of the 
heat applied, become hotter and consequently lighter than the 
layer below it, and colder and consequently heavier than the 
layer above it. It therefore cannot ascend, because it is too 
heavy ; nor can it descend, because it is too light. But the 
sea in equatorial regions is heated from above, and not from 
below ; consequently the water at the bottom does not rise to 
the surface at the equator in virtue of any heat which it 
receives. A layer cf water can never raise the temperature of 
a layer below it to a higher temperature than itself; and since 
it cannot do this, it cannot make the layer imder it lighter than 
itself. That which raises Hhe water at the equator, according 
to Dr. Carpenter's theory, must be the downward pressure of 
the polar column. When water flows down the slope from the 
equator to the pole, the polar column, as we have seen, becomes 
too heavy and the equatorial column too light ; the former then 
sinks and the latter rises. It is the sinking of the polar 
column which raises the equatorial one. When the polar 
column descends, as much water is pressed in underneath the 
equatorial column as is pressed from underneath the polar 
oolunm. If one foot of water is pressed from under the 
polar column, a foot of water is pressed in under the equa- 
torial column. Thus, when the polar column sinks a foot, 
the equatorial column rises to the same extent. The equa- 
torial water continuing to flow down the slope, the polar 
column descends : a foot of water is again pressed from under- 
neath the polar column and a foot pressed in under the equa- 
torial. As foot after foot is thus removed from the bottom of 
the polar column while it sinks, foot after foot is pushed in under 



164 CLIMATE AND TIME. 

tlie equatorial column while it rises ; so by this means the water 
at the surface of the ocean in polar regions descends to the 
bottom, and the water at the bottom in equatorial regions 
ascends to the surface — the effect of solar heat and polar oold 
continuing) of course, to maintain the surfSu^ of the ocean in 
equatorial regions at a higher level than at the poles, and thus 
keeping up a constant state of disturbed equilibrium. Or, to 
state the matter in Dr. Carpenter's own words, " The cold and 
dense polar water, as it flows in at the bottom of the equatorial 
column, will not directly take the place of that which has been 
drafted off from the surface ; but this place will be filled by 
the rising of the whole superincumbent column, which, being 
warmer, is also lighter than the cold stratum beneath. Every 
new arrival from the poles will take its place below that which 
precedes it, since its temperature will have been less affected by 
contact with the warmer water above it. In this way an 
ascending movement will be imparted to the whole equatorial 
column, and in due course every portion of it will come under 
the influence of the surface-heat of the sun."* 

But the agency which raises up the water of the under 
current to the surface is the pressure of the polar column. The 
equatorial column cannot rise directly by means of gravity. 
Gravity, instead of raising the column, exerts all its powers to 
prevent its rising. Gravity here is a force acting against the 
current. It is the descent of the polar column, as has been 
stated, that raises the equatorial column. Consequently the 
entire amount of work performed by g^a^'ity in pulling down 
the polar column is spent in raising the equatorial column. 
Gravity performs exactly as much work in preventing motion 
in the equatorial column as it performs in producing motion in 
the polar column ; so that, so far as the vertical parts of Dr. 
Carpenter's circulation are concerned, gravity may be said 
neither to produce motion nor to prevent it. And this remark, 
be it observed, applies not only to P O and E Q, but also to the 
parts P' P and E E' of the two columns. When a mass of 

• Proceedings of the Royal Societv, vol. xix., p. 215. 



THE GRAVITATION THEORY. 165 

water E £', 8a j one foot deep^ is remoyed off the equatorial 
column and plaoed upon the polar column, the latter column ia 
then heavier than the former by the weight of two feet of 
water. Grayitj then exerts more force in pulling the polar 
column down than it does in preyenting the equatorial column 
firom rising; and the consequence is that the polar column 
begins to descend and the equatorial column to rise. But as the 
polar column continues to descend and the equatorial to rise, 
the power of gravity to produce motion in the polar column 
diminishes, and the power of gravity to prevent motion in the 
equatorial colimm increases ; and when P' descends to P and E' 
rises to E, the power of gravity to prevent motion in the 
equatorial column is exactly equal to the power of gravity to 
produce motion in the polar column, and consequently motion 
ceases. It therefore follows that the entire amount of work 
performed by the descent of P' P is spent in raising E' E 
against gravity. 

It follows also that inequalities in the sea-bottom cannot in 
any way aid the circulation ; for although the cold under 
current should in its progress come to a deep trough filled with 
water less dense than itself, it would no doubt sink to the 
bottom of the hollow ; yet before it could get out again as much 
work would have to be performed against gravity as was per- 
formed by gravity in sinking it. But whilst inequalities in the 
bed of the ocean would not aid the current, they would never- 
theless very considerably retard it by the obstructions which 
they would offer to the motion of the water. 

We have been assuming that the weight of P' P is equal to 
that of E E' ; but the mass P' P must be greater than E E' 
because P' P has not only to raise E E', but to impel the under 
current — to push the water along the sea-bottom from the pole 
to the equator. So we must have a mass of water, in addition 
to P' P, placed on the polar column to enable it to produce the 
under current in addition to the raising of the equatorial column. 

It follows also that the amount of work which can be per- 
formed by gravity depends entirely on the difference of tempo- 



166 CLIMATE AND TIME. 

ratnrc betvrcen the equatorial and tlie polar waters, and ia 
wholly independent of the way in whicH the temperature may 
decrease from the equator to the poles. Suppose, in agree- 
ment with Dr. Carpenter's idea,* that the equatorial Heat and 
polar cold should be confined to limited areas, and that throngh 
the intermediate space no great difference of temperature sihoald 
prevaiL 8uch an arrangement as this would not increase the 
amount of work which gravity could perform ; it would simply 
make the slope steeper at the two extremes and flatter in the 
interyening space. It would no doubt aid the surface-flow of 
the water near the equator and the poles, but it would retard 
in a corresponding degree the flow of the water in the inter- 
mediate regions. In short, it would merely destroy the unifor- 
mity of the slope without aiding in the least degree the general 
motion of the water. 

It is therefore demonstrable that ihe energy derived from the 
full slope, whatever that slope may be, comprehemlH all that can pos- 
rihly he ohtained from gravity. 

It cannot bo urged as an objection to what has been advanced 
that I have determined simply the amount of the force acting 
on the water at the surface of the ocean and not that on the 
water at all dfjpths — that I have estimated the amount of work 
which gravity can perform on a given quantity of water at the 
8urfac(», but not the total amount of work which gravity can 
perform on the entire ocean. This objection will not stand, 
b(»('auH«i it iM at the surface of the ocean where the greatest 
diirrroiirn of tcniperature, and consequently of density, exists 
bi'twcHMi Wn) cqtniiorial and polar waters, and therefore there 
that Kravity rxorts its greatest force. And if gravity be 
unablr to inovo the water at the surface, it is much less able to 
do HO under tlu» Hurface. So far as the question at issue is 
concrnifd, any calculations as to the amount of force exerted 
bv gravity at various depths are needless. 

It is maintained also that the winds cannot produce a vertical 
current, except under some very peculiar conditions. We have 

• NntuT$ for July 6, 1871. 



THE GRAVITATION TIIEORF. 167 

already seen that, according to Dr. Carpenter's theory, the 
vertical motion is caused by the water flowing off the equatorial 
column, down the slope, upon the polar column, thus des toy- 
ing the equilibrium between the two by diminishing the weight 
of the equatorial column and increasing that of the polar column. 
In order that equilibrium may be restored, the polar column 
sinks and the equatorial one rises. I^ow must not the same 
effect occur, supposing the water to be transferred from the one 
column to the other, by the influence of the winds instciid of 
by the influence of gravity P The vertical descent and ascent 
of these columns depend entirely upon the difference in their 
weights, and not upon the nature of the agency which makes 
this difference. So far as difference of weight is concerned, 
2 feet of water, propelled down the slope from the equa- 
torial column to the polar by the winds, will produce just tl^o 
same effect as though it had been propelled by gravity. If 
vertical motion follows as a necessary consequence from a 
transference of water from the equator to the poles by gravity, 
it follows equally as a necessary consequence from the same 
transference by the winds; so that one is not at liberty to 
advocate a vertical circulation in the one case and to deny it 
in the other. 

Gravitation Theory of the Gibraltar Current, — If difference of 
specific gravity fails to account for the currents of the ocean in 
general, it certainly fails in a still more decided manner to 
account for the Gibraltar current. The existence of the sub- 
marine ridge between Capes Trafalgar and Spartel, as was 
shown in the Phil. Mag. for October, 1871, p. 269, affects 
currents resulting from difference of specific gravity in a manner 
which does not seem to have suggested itself to Dr. Carpenter. 
The pressure of water and other fluids is not like that of a solid 
— not like that of the weight in the scale of a balance, simply 
a downward pressure. Fluids press downwards like the solids, 
but they also press laterally. The pressure of water is hydro- 
static. If we fill a basin with water or any other fluid, the 
fluid remains in perfect equilibrium, provided the sides of the 



i66 CLIMATE AND TIME. 

rature between the equatorial and tlie polar waters, and if 
wholly independent of the way in which the temperature maj 
decrease from the equator to the poles. Suppose, in agree- 
ment with Dr. Carpenter's idea,* that the equatorial heat and 
polar cold should be confined to limited areas, and that through 
the intermediate space no great difference of temperature ahould 
prevaiL Such an arrangement as this would not increase the 
amount of work which gravity could perform ; it would simply 
make the slope steeper at the two extremes and flatter in the 
intervening space. It would no doubt aid the surface-flow of 
the water near the equator and the poles, but it would retard 
in a corresponding degree the flow of the water in the inter- 
mediate regions. In short, it would merely destroy the unifor- 
mity of the slope without aiding in the least degree the general 
motion of the water. 

It is therefore demonstrable that the energy derived from the 
full slope f whatever that slope may be, comprehendji all that can pos- 
ribly he obtained from gravity. 

It cannot be urged as an objection to what has been advanced 
that I have determined simply the amount of the force acting 
on the water at the surface of the ocean and not that on the 
water at all depths — that I have estimated the amount of work 
which gravity can perform on a given quantity of water at the 
surface, but not the total amount of work which gravity can 
perform on the entire ocean. This objection will not stand, 
because it is at the surface of the ocean where the greatest 
diflerence of temperature, and consequently of density, exists 
between the equatorial and polar waters, and therefore there 
that gravity exerts its greatest force. And if gravity be 
imable to move the water at the surface, it is much less able to 
do so under the surface. So far as the question at issue is 
concerned, any calculations as to the amount of force exerted 
by gravity at various depths are needless. 

It is maintained also that the winds cannot produce a vertical 
current except under some very peculiar conditions. We have 

• Natur$ for July 6, 1871. 



THE GRAVITATION THEORY. 167 

already seen that, according to Dr. Carpenter's theory, the 
vertical motion is caused by the water flowing off the equatorial 
colomn, down the slope, upon the polar column, thus des^/roy- 
ing the equilibrium between the two by diminishing the weight 
of the equatorial column and increasing that of the polar column. 
In order that equilibrium may be restored, the polar column 
sinks and the equatorial one rises, ^ow must not the same 
effect occur, supposing the water to be transferred from the one 
column to the other, by the influence of the winds instead of 
by the influence of gra\'ity P The vertical descent and ascent 
of these columns depend entirely upon the difference in their 
weights, and not upon the nature of the agency which makes 
this difference. So far as difference of weight is concerned, 
2 feet of water, propelled down the slope from the equa- 
torial colimm to the polar by the winds, will produce just the 
same effect as though it had been propelled by gravity. If 
vertical motion follows as a necessary consequence from a 
transference of water from the equator to the poles by gravity, 
it follows equally as a necessary consequence from the same 
transference by the winds; so that one is not at liberty to 
advocate a vertical circulation in the one case and to deny it 
in the other. 

Chravitation Theory of the Gibraltar Current. — If difference of 
specific gravity fails to account for the currents of the ocean in 
general, it certainly fails in a still more decided manner to 
account for the Gibraltar current. The existence of the sub- 
marine ridge between Capes Trafalgar and Spartcl, as was 
shown in the Phil. Mag. for October, 1871, p. 269, affects 
currents resulting from difference of specific gravity in a manner 
which does not seem to have suggested itself to Dr. Carpenter. 
The pressure of water and other fluids is not like that of a solid 
— ^not like that of the weight in the scale of a balance, simply 
a downward pressure. Fluids press downwards like the solids, 
but they also press laterally. The pressure of water is hydro- 
static. If we fill a basin with water or any other fluid, the 
fluid remains in perfect equilibrium, provided the sides of the 



i66 CLIMATE AND TIME. 

rature between the equatorial and the polar waters, and ii 
wholly independent of the way in which the temperature may 
decrease from the equator to the poles. Suppose, in agre^ 
ment with Dr. Carpenter's idea,* that the equatorial heat and 
polar cold should be confined to limited areas, and that through 
the intermediate space no great difEerence of temperature should 
prevail. Such an arrangement as this would not increase the 
amoimt of work which gravity could perform ; it would simply 
make the slope steeper at the two extremes and flatter in the 
intervening space. It would no doubt aid the surface-flow of 
the water near the equator and the poles, but it would retard 
in a corresponding degree the flow of the water in the inter- 
mediate regions. In short, it would merely destroy the unifor- 
mity of the slope without aiding in the least degree the general 
motion of the water. 

It is therefore demonstrable that the energy derived from the 
full dope, whatever that slope mat/ be, cowprchendji all that can pon- 
sibly be obtained from gravity. 

It cannot be urged as an objection to what has been advanced 
that I have determined simply the amount of the force acting 
on the water at the surface of the ocean and not that on the 
water at all depths — that I have estimated the amount of work 
which gravity can perform on a given quantity of water at the 
surface, but not the total amount of work which gravity can 
perform on the entire ocean. This objection will not stand, 
because it is at the surface of the ocean where the greatest 
difference of temperature, and consequently of density, exists 
between the equatorial and polar waters, and therefore there 
that gravity exerts its greatest force. And if gravity be 
unable to move the water at the surface, it is much less able to 
do so under the surface. So far as the question at issue is 
concerned, any calculations as to the amount of force exerted 
by gravity at various depths are needless. 

It is maintained also that the winds cannot produce a vertical 
current except under some very peculiar conditions. We have 

• Nature for July 6, 1871. 



THE GRA VITA TION THEORY. 1 67 

already seen that, according to Dr. Carpenter's theory, the 
▼ertical motion is caused by the water flowing off the equatorial 
colamn, down the slope, upon the polar column, thus destroy- 
ing the equilibrium between the two by diminishing the weight 
of the equatorial column and increasing that of the polar colunm. 
In order that equilibrium may be restored, the polar column 
sinks and the equatorial one rises. Now must not the same 
effect occur, supposing the water to be transferred from the one 
colamn to the other, by the influence of the winds instead of 
by the influence of gravity P The vertical descent and ascent 
of these columns depend entirely upon the difference in their 
weights, and not upon the nature of the agency which makes 
this difference. So far as difference of weight is concerned, 
2 feet of water, propelled down the slope from the equa- 
torial column to the polar by the winds, will produce just the 
same effect as though it had been propelled by gravity. If 
vertical motion follows as a necessary consequence from a 
transference of water from the equator to the poles by gravity, 
it follows equally as a necessary consequence from the same 
transference by the winds; so that one is not at liberty to 
advocate a vertical circulation in the one case and to deny it 
in the other. 

OrapUation Theory of the Qihraltar Current, — ^If difference of 
specific gravity fails to account for the currents of the ocean in 
general, it certainly fails in a still more decided manner to 
account for the Gibraltar current. The existence of the sub- 
marine ridge between Capes Trafalgar and Spartel, as was 
shown in the Phil. Mag. for October, 1871, p. 269, affects 
currents resulting from difference of specific gravity in a manner 
which does not seem to have suggested itself to Dr. Carpenter. 
The pressure of water and other fiuids is not like that of a solid 
— ^not like that of the weight in the scale of a balance, simply 
a downward pressure. Fluids press downwards like the solids, 
but they also press laterally. The pressure of water is hydro- 
static. If we fill a basin with water or any other fluid, the 
fluid remains in perfect equilibriirai, provided the sides of the 



1 68 CLIMATE AND TIME. 

basin be saJBSciently strong to resist the pressure. The Medi« 
terranean and Athintie, up to the level of the submarine ridge 
referred to, may be regarded as huge basins, the sides of which 
are sufficiently strong to resist all pressure. It follows that, how- 
ever much denser the water of the Mediterranean may be than 
that of the Atlantic, it is only the water above the level of the 
ridge that can possibly exercise any influence in the way of 
disturbing equilibrium, so as to cause the level of the Medi- 
terranean to stand lower than that of the Atlantic. The water 
of the Atlantic below the level of this ridge might be as light 
as air, and that of the Mediterranean as heavy as molten lead, 
but this could produce no disturbance of equilibrium ; and if 
there be no diflerence of density between the Atlantic and the 
Mediterranean waters from the surface down to the level of 
the top of the ridge, then there can be nothing to produce the 
circulation which Dr. Carpenter infers. Suppose both basins 
empty, and dense water to be poured into the Mediterranean, 
and water less dense into the Atlantic, until they are both filled 
up to the level of the ridge, it is evident that the heavier water 
in the one basin can exercise no influence in raising the level 
of the lighter water in the other basin, the entire pressure being 
borne by the sides of the basins. But if we continue to pour in 
water till the surface is raised, say one foot, above the level of 
the ridge, then there is nothing to resist the lateral pressure of 
this one foot of water in the Mediterranean but the counter 
pressure of the one foot in the Atlantic. But as the Mediter- 
ranean water is denser than the Atlantic, this one foot of water 
will consequently exert more pressure than the one foot of water 
of the Atlantic. We must therefore continue to pour more 
water into the Atlantic until its lateral pressure equals that of 
the Mediterranean. The two seas will then be in equilibrium, 
but the surface of the Atlantic will of course be at a higher 
level than the surface of the Mediterranean. The difference 
of level will be proportionate to the difference in density of the 
waters of the two seas. But here we come to the point of 
importance. In determining the difference of level between 



THE GRAVITATION THEORY. 169 

tlie two seaSy or, which is the same thing, the difference of level 
between a column of the Atlantic and a column of the Mediter- 
ranean, we must take into consideration only the water tchieh 
b'ea above the kvel of the ridge. If there be one foot of water 
above the ridge, then there is a difference of level proportionate 
to the difference of pressure between the one foot of water of 
the two seas. If there be 2 feet, 3 feet, or any number of feet 
of water above the level of the ridge, the difference of level is 
proportionate to the 2 feet, 3 feet, or whatever number of feet 
there may be of water above the ridge. If, for example, 13 
should represent the density of the Mediterranean water and 
12 the density of the Atlantic water, then if there were one foot 
of water in the Mediterranean above the level of the ridge, 
there would require to be one foot one inch of water in the 
Atlantic above the ridge in order that the two might be in 
equilibrium. The difference of level would therefore be one 
inch. If there were 2 feet of water, the difference of level 
would be 2 inches ; if 3 feet, the difference would be 3 inches, 
and so on. And this would follow, no matter what the actual 
depth of the two basins might be ; the water below the level of 
the ridge exercising no influence whatever on the level of the 
surface. 

Taking Dr. Carpenter's own data as to the density of the 
Mediterranean and Atlantic waters, what, then, is the difference 
of density ? The submarine ridge comes to within 167 fathoms 
of the surface ; say, in round numbers, to within 1,000 feet. 
What are the densities of the two basins down to the depth of 
1,000 feet? According to Dr. Carpenter there is little, if any, 
difference. His own words on this point are these : — " A 
comparison of these results leaves no doubt that there is an 
excess of salinity in the water of the Mediterranean above that 
of the Atlantic ; but that this excess is slight in the surface- 
water, whilst somewhat greater in the deeper water'* (§ 7). 
"Again, it was found by examining samples of water taken 
from the surface, from 100 fathoms, from 250 fathoms, and 
from 400 fathoms respectively, that whilst the fir$t two had the 



170 CLIMATE AND TIME. 

eharacteristic temperature and density of Atlantic water ^ the last 
two had the characteristics and density of Mediterranean 
water'' (§ 13). Here, at least to the depth of 100 fathoms or 
600 feet, there is little difference of density between the waters 
of the two basins. Consequently down to the depth of 600 
feet, there is nothing to produce any sensible disturbance of 
equilibrium. If there be any sensible disturbance of equilibrium, 
it must be in consequence of difference of density which may 
exist between the depths of 600 feet and the surface of the ridge. 
We have nothing to do with any difference which may exist 
between the water of the Mediterranean and the Atlantic below 
the ridge; the water in the Mediterranean basin may be as 
heavy as mercury below 1,000 feet : but this can have no effect 
in disturbing equilibrium. The water to the depth of 600 feet 
being of the same density in both seas, the length of the two 
columns acting on each other is therefore reduced to 400 feet — 
that is, to that stratum of water lying at a depth of from 600 
to the surface of the ridge 1,000 feet below the surface. But, 
to give the theory full justice, we shall take the Mediterranean 
stratum at the density of the deep water of the Mediterranean, 
which he found to be about 1*029, and the density of the 
Atlantic stratum at 1*026. The difference of density between 
the two columns is therefore *003. Consequently, if the height 
of the Mediterranean column bo 400 feet, it will be balanced by 
the Atlantic column of 401*2 feet; the difference of level 
between the Mediterranean and the Atlantic cannot therefore 
be more than 1*2 foot. The amount of work that can be per- 
formed by gravity in the case of the Gibraltar current is little 
more than one foot-pound per pound of water, an amount of 
energy evidently inadequate to produce the current. 

It is true that in his last expedition Dr. Carpenter found the 
bottom- water on the ridge somewhat denser than Atlantic 
water at the same depth, the former being 1*0292 and the latter 
1*0265 ; but it also proved to be denser than Mediterranean 
water at the same depth. He foimd, for example, that " the 
dense Mediterranean water lies about 100 fathoms nearer the 



THE GRAVITATION THEORY. 171 

surface over a 300-fathoms bottom, than it does where the 
bottom sinks to more than 500 fathoms " (§ 51). But any 
excess of density which might exist at the ridge could have no 
tendency whatever to make the Mediterranean column pre- 
ponderate over the Atlantic column, any more than could a 
weight placed over the fulcrum of a balance have a tendency 
to make the one scale weigh down the other. 

If the objection referred to be sound, it shows the mechanical 
impossibility of the theory. It proves that whether there be 
an under current or not, or whether the dense water lying in 
the deep trough of the Mediterranean be carried over the sub- 
marine ridge into the Atlantic or not, the explanation offered 
by Dr. Carpenter is one which cannot be admitted. It is 
incumbent on him to explain either (1) how the almost in- 
finitesimal difference of density which exists between the 
Atlantic and Mediterranean columns down to the level of the 
ridge can produce the upper and under currents carrying 
the deep and dense water of the Mediterranean over the ridge, 
or (2) how all this can be done by means of the difference of 
density which exists below the level of the ridge.* What the 
true cause of the Gibraltar current really is will be considered 
in Chap. XIU. 

The Baltic Current. — The entrance to the Baltic Sea is in 
some places not over 50 or 60 feet deep. It follows, therefore, 
from what has already been proved in regard to the Gibraltar 
current, that the influence of gravity must be even still less in 
causing a current in the Baltic strait than in the Gibraltar 
strait. 

• Since the above objection to the Gravitfition Theory of the Gibraltar CurreTit 
was advjinced three \ 'jurs ago, Dr. Carpenter appears to have abandoned the theory 
to a great extent. He now admits (Proceedings of Royal Geographical Society, 
vol. xviii., pp. 319 — 334, 1874) that the current ia almost wholly duo not to 
difference of specific eriuvity, but to an excess of evaporation in the Mediterranean 
over the return by rain and rivers. 



CHAPTER X. 

KXAMINATIOX OF THE GRAVITATION THEORY OF OCSANIC CIBCULA- 
TION. DR. carpenter's THEORY. — OBJECTIONS CONSIDBBBD. 

Modui Operandi of the Matter. — Polar Cold considered by Dr. Carpenter the 
Primum Mobile. — Supposed Influence of Heat derived from the Earth'e 
Crust. — Circulation without Difference of Level. — ^A Confusion of Ideas in 
Reference to the supposed Agency of Polar Cold. — ^M. Dubuat's Experi- 
ments. — A Begging of the Question at Issue. — Pressure as a Cause of Circa- 
lation. 

In the foregoing chapter, the substance of which appeared in 
the Phil. Mag. for October, 1871, I have represented the 
manner in which difference of specific gra\'ity produces circula- 
tion. But Dr. Carpenter appears to think that there are some 
important points which I have overlooked. These I shall now 
proceed to consider in detail. 

" Mr. CroU's whole manner of treating the subject,*' he 
says, "is so different from that wliich it appears to me to 
require, and he has so completely misapprehended my own 
view of the question, that I feel it requisite to present this in 
fuller detail in order that physicists and mathematicians, 
having both sides fully before them, may judge between 
us" (§26).* 

He then refers to a point so obvious as hardly to require 
consideration, viz., the effect which results when the surface of 
the entire area of a lake or pond of water is cooled. The whole 
of the surface-film, being chilled at the same time, sinks through 
the subjacent water, and a new film from the warmer layer 
immediately beneath. the surface rises into its place. This 
being cooled in its turn, sinks, and so on. He next considers 

• Proceedings of Royal Society, Na 138, § 2G. 



THE GRAVITATION THEORY, 173 

what takes place when only a portion of the surface of the 
pond is cooledy and shows that in this case the surface-film 
whicli descends is replaced not fironx beneath, but by an inflow 
from the neighbouring area. 

" That such must be the case," says Dr. Carpenter, ** appears 
to me so self-eyident that I am surprised that any person con« 
yersant with the principles of physical science should hesitate 
in admitting it, still more that he should explicitly deny it. 
But since others may feel the same difficulty as Mr. Croll, it 
may be worth while for me to present the case in a form of yet 
more elementary simplicity" (§ 29). 

Then, in order to show the mode in which the general 
ooeanic circulation takes place, he supposes two cylindrical 
▼easels, W and C, of equal size, to be filled with sea-water. 
Cylinder W represents the equatorial column, and the water 
contained in it has its temperature maintained at 60^ ; whilst 
the water in the other cylinder C, representing the polar 
column, has its temperature maintained at 30^ by means of the 
constant application of cold at the top. Free communication 
is maintained between the two cylinders at top and bottom; 
and the water in the cold cylinder being, in virtue of its low 
temperature, denser than the water in the warm cylinder, the 
two columns are therefore not in static equilibrium. The cold, 
and hence heavier column tends to produce an outflow of water 
from its bottom to the bottom of the warm column, which out- 
flow is replaced by an inflow from the top of the warm column 
to the top of the cold column. In fact, we have just a simple 
repetition of what he has given over and over again in his 
various memoirs on the subject. But why so repeatedly enter 
into the modus operandi of the matter ? Who feels any diffi- 
culty in understanding how the circulation is produced ? 

Polar Cold conaUerid by Dr. Carpenter the Prifnuni Mohik. — 
It is evident that Dr. Carpenter believes that he has found in 
polar cold an agency the potency of which, in producing a 
general oceanic circulation, has been overlooked by physicists ; 
and it is with the view of developing his ideas on this subject 



174 CLIMATE AND TIME. 

that he haa entered so fully and bo frequently into the exposU 
tion of his theory. " If I have myself done anything/' he 
says, " to strengthen the doctrine, it has been by showing that 
polar cold, rather than equatorial heat, is the primum mMIe of 
this circulation."* 

The influence of the sun in heating the waters of the inter- 
tropical seas is, in Dr. Carpenter's manner of Tiewing the 
problem, of no great importance. The efficient cause of motion 
he considers resides in cold rather than in fieat. In £act, he 
even goes the length of maintaining that, as a power in the 
production of the general interchange of equatorial and polar 
water, the effect of polar cold is so much superior to tlmt of 
inter-tropical heat, that the influcnca of the latter may be 
practically disregarded. 

" Suppose two basins of ocean-water," he says, " connected 
by a strait to be placed under such different climatic conditions 
that the surface of one is exposed to the heating influence of 
tropical sunshine, whilst the surface of the other is subjected to 
the extreme cold of the simless polar winter. The effect of the 
surface-heat upon the water of the tropical basin will be for the 
most part limited (as I shall presently show) to its uppermost 
stratum, and may here be practically disregarded.*' f 

Dr. Caq)enter'8 idea regarding the efficiency of cold in 
producing motion seems to me to be not only opposed to the 
generally received views on the subject, but wholly irreconcile- 
able with the ordinary principles of mechanics. In fact, there 
are so many points on which Dr. Carpenter's theory of a 
" General Vertical Oceanic Circulation " differs from the gene- 
rally received views on the subject of circulation by means of 
difference of specific gravity, that I have thought it advisable 
to enter somewhat minutely into the consideration of the 
mechanics of that theory, the more so as he has so repeatedly 
asserted that eminent physicists agree with what he has advanced 
on the subject. 

According to the generallj' received theory, the circulation 

• Frococdings of Royal Geographicul Society, January 9, 1871. f Ibid. 



THE GRAVITATION THEORY, 175 

IB due to the difference of dermty between the sea in equatorial 
and polar regions. The real efficient cause is gravity ; but 
grarity cannot act when there is no difference of specific gravity. 
If the sea were of equal density from the poles to the equator, 
gravity could exercise no influence in the production of circu- 
lation ; and the influence which it does possess is in proportion 
to the difference of density. But the difference of density 
between equatorial and polar waters is in turn due not abso- 
lutely either to polar cold or to tropical heat, but to both — 
or, in other words, to the difference of temperature between the 
polar and equatorial seas. This difference, in the very nature 
of things, must be as much the result of equatorial heat as of 
polar cold. If the sea in equatorial regions were not being 
heated by the sun as rapidly as the sea in polar regions is 
being cooled, the difference of temperature between them, and 
consequently the difference of density, would be diminishing, 
and in course of time would disappear altogether. As has 
already been shown, it is a necessary consequence that the 
water flowing from equatorial to polar regions must be com- 
pensated by an equal amount flowing from polar to equatorial 
regions. Now, if the water flowing from polar to equatorial 
regions were not being heated as rapidly as the water flowing 
from equatorial to polar regions is being cooled, the equatorial 
seas would gradually become colder and colder uutil no sensible 
difference of temperature existed between them and the polar 
oceans. In fact, equality of the two rates is necessary to the 
very existence of such a general circulation as that advocated 
by Dr. Carpenter. If he admits that the general interchange 
of equatorial and polar water advocated by him is caused by 
the difference of density between the water at the equator and 
the pf;lcs, resulting from difference of temperature, then he 
must admit also that this difference of density is just as much 
due to the heating of the equatorial water by the sun as it is to 
the cooling of the polar water by radiation and other means — or, 
in other words, that it is as much due to equatorial heat as to 
polar cold. And if so, it cannot be true that polar cold rather 

9 



176 CLIMATE AND TIME. 

than equatorial heat is the "primum mobile ** of this ciiculatioQ ; 
amd far less can it be true that the heating of the equatorial 
water by the sun is of so little importance that it may be 
" practically disregarded." 

Supposed Influence of Heat derived from the EartK% Crust — 
There is, according to Dr. Carpenter, another agent concerned 
in the production of the general oceanic circulation, yiz., the 
heat derived by the bottom of the ocean from the crust of the 
eartK* We have no reason to believe that the quantity of 
internal heat coming through the earth's crust is greater in 
one part of the globe than in another ; nor have we any grounds 
for concluding that the bottom of inter-tropical seas receives 
more heat from the earth's crust than the bottom of those in 
polar regions. But if the polar seas receive as much heat from 
this source iis the seas within the tropics, then the difference of 
density between the two cannot possibly be due to heat received 
from the earth's crust ; and this being so, it is mechanically 
impossible that internal heat can be a cause in the production 
of the general oceanic circuLition. 

Circulation without Difference of Level, — There is another part 
of the theory which appears to me irreconcilable with mecha- 
nics. It is maintained that this general circulation takes place 
without any difference of level between the equator and the 
poles. Referring to the ciise of the two cylinders W and C, 
which represent the equatorial and polar columns respectively, 
Dr. Carpenter says : — 

" The force which will thus lift up the entire column of 
water in W is that which causes the descent of the entire 
column in C, namely, the excess of gravity constantly acting in 
C, — the levels of the two columns, and consequently their 
heights, being maintained at a constant equality by the free 
passage of surface-water from W to C." 

•' The whole of Mr. CrolFs discussion of this question, how- 
ever,'* he continues, " proceeds upon the assumption that the 
leyels of the polar and equatorial columns are not kept at an 

{{ 20, 84 ; tbo Brit. Afsoo. Report for 1872, p. 49, and other placei. 



THE GRAVITATION THEORY, 



^Tt 



tqwaJUy^ &c/' (S 30.) And again, " Now, so far from asserting 
(as Captain Maury has done) that the trifling difference of level 
arising from inequality of temperature is adequate to the pro- 
duction of ocean-currents, I simply affirm that as fast as the 
level is disturbed by change of temperature it will be restored 
by gravity." (§ 23.) • 

In order to understand more clearly how the circulation 
under consideration cannot take place without a difference of 
level, let W E (Fig. 3) represent the equatorial column, and C P 
the polar column. The equatorial column is warmer than the 
polar column because it receives more heat from the sun than 
the latter ; and the polar is colder than the equatorial column 



Fig. 3. 



IE 



w 



because it receives fc««. The difference in the density of the 
two columns results from their difference of temperature ; and 
the difference of temperature results in turn from the difference 
in the quantity of heat received from the sun by each. Or, to 
express the matter in other words, the difference of density 
(and consequently the circulation under consideration) is due 
to the excess of heat received from the sun by the equatorial 
over that received by the polar column ; so that to leave out of 
account the superheating of the inter-tropical waters by the sun 
is to leave out of account the very thing of all others that is 
absolutely essential to the existence of the circulation. The 
water being assumed to be the same in both columns and differ- 
ing only as regards temperature, and the equatorial column 

* See also to the sume cfifect Brit. Assoc. Report, 1872, p. 50. 



178 CLIMATE AND TIME. 

posseesmg more heat than the polar, and being therefore leai 
dense than the latter, it follows, in order that the two columns 
may be in static equilibrium, that the surface of the equa- 
torial column must stand at a higher level than that of the 
polar. This produces the slope W C from the equator to the 
pole. The extent of the slope ^411 of course depend upon 
the extent of the difference of their temperatures. But, as 
was shown on a former occasion,* it is impossible that statio 
equilibrium can ever be fully obtained, because the slope occa- 
sioned by the elevation of the equatorial column above the 
polar produces whjit we may be allowed to call a molecular 
disturbance of equilibrium. The surface of the ocean, or the 
molecules of water lying on the slope, are not in a position of 
equilibrium, but tend, in virtue of gravity, to roll down the 
slope in the direction of the polar column C. It will be 
observed that the more we gain of static equilibrium of the 
entire ocean the greater is the slope, and consequently the 
greater is the disturbance of molecular equilibrium; and, vice 
rersd, the nmre molecular equilibrium is restored by the reduc- 
tion of the slope, the greater is the disturbance of static equili- 
brium. If in tliercfore alHohifchj i/nposMIe that loth conditions of 
equilibrium can be fulfilled at the same time so long as a difference 
of trmprraturr exists bet men the two col"mus. Aud this conclu- 
sion holds true even thougli we should a^-sume water to be a 
perfect fluid absolutely devoid of viscosity. It fullows, there- 
fore, that a general oceanic circulation without a difference of 
level is a mrchanieal impossibitift/. 

In a case of actual circulation due to difference of g^a^'ity, 
there is alwavs a con>t.int disturbance of both static and mole- 
cular equilibrium. Cijlumu C is always higher and column W 
always lower than it ought to be were the twt) in equilibrium : 
but they never can be at the same level. 

It is quite conceivable, of course, that thv* two conditions of 
equilibrium may be fulfilled alternately. We can conceive 
^■wn" C remaining stationary till the water flowing from 

• rhil. Mag. fur Oct 1871. 



THE GRAVITATION THEORY. 179 

columxL W has restored the level. And after the level is re- 
stored we can conceive the polar column C sinking and the 
equatorial column W rising till the two perfectly balance each 
other. Such a mode of circulation, consisting of an alternate 
sur&ce-flow and vertical descent and ascent of the columns, 
though conceivable, is in reality impossible in nature ; for there 
are no means by which the polar column C could be supported 
from sinking till the level had been restored. But Dr. Car- 
penter does not assume that the general ocennic circulation 
takes place in this intermitting manner ; according to him, the 
circidation is constant. He asserts that there is a "continual 
transferrence of water from the bottom of C to the bottom of W, 
and from the top of W to the top of C, with a constant descend- 
ing movement in C and a constant ascending movement in 
W " (§ 29). But such a condition of things is irreconcilable 
with the idea of " the levels of the two columns, and conse- 
quently their heights, being maintained at a constant equality ' 
(S 29). 

Although Dr. Carpenter does not admit the existence of a 
permanent difference of level between the equator and the pole, 
he nevertheless speaks of a depression of level in the polar basin 
resulting from the contraction by cooling of the water flowing 
into it. This reduction of level induces an inflow of water from 
the surrounding area; "and since what is drawn away,'* to 
quote his own words, " is supplied from a yet greater distance, 
the continued cooling of the surface-stratum in the polar basin 
will cause a ' set ' of waters towards it, to be propagated back- 
wards through the whole intervening ocean in communication 
with it until it reaches the tropical area.'* The slope produced 
between the polar basin and the surrounding area, if sufficiently 
great, will enable the water in the surrounding area to flow 
polewards ; but unless this slope extend to the equator, it will 
not enable the tropical waters also to flow polewards. One of 
two things mKjessarily follows : either the slope extends from 
the equator to the pole, or water can flow from the equator to 
the pole without a slope. If Dr. Carpenter maintains the 



iSo CLIMATE AND TIME. 

former, he contradicts himself; and if he adepts the latter, ha 
contradicts an obvious principle of mechanics. 

A Confusion of Ideas in Reference to the supposed Agency o) 
Polar Cold. — It seems to me that Dr. Carpenter has been some- 
what misled bv a slight confusion of ideas in reference to the 
supposed agency of polar cold. This is brought out forcibly is 
the following passage from his memoir in the Proceedings of 
the Royal Geographical Society, vol. xv. 

" Mr. CroU, in arguing against the doctrine of a general 
oceanic circulation sustained by difference of temperature, and 
justly maintaining that such a circulation cannot be produced by 
the application of heat at the surface,, has entirely ignored the 
agency of cold." 

It is here supposed that there are two agents at work in the 
production of the general oceanic circulation. The one agent 
is heaty acting at the equatorial regions ; and the other agent 
is cold^ acting at the polar regions. It is supposed that the 
agency of cold is far more powerful than that of heat. In fact 
so trifling is the agency of equatorial heat in comparison with 
that of polar cold that it may be " practically disregarded " — 
left out of account altogether, — polar cold being the primum 
mobile of the circulation. It is supposed also that I have con- 
sidered the efEciency of one of the agents, viz., heat, and found 
it totally inadequate to produce the circulation in question ; 
and it is admitted also that my conclusions are perfectly correct. 
But then I am supposed to have left out of account the other 
agent, viz., polar cold, the only agent possessing real potency. 
Had I taken into account polar cold, it is supposed that I 
should have found at once a cause perfectly adequate to produce 
the required effect. 

This is a fair statement of Dr. Carpenter's views on the sub- 
ject ; I am unable, at least, to attach any other meaning to his 
words. And I have no doubt thev are also the views which 
have been adopted by those who have accepted his theory. 

It must be sufficiently evident from what has already been 
■tilled, ihat the notion of there being two separate agents at 



THE GRAVITATION THEORY. i8i 

work producmg circulation, namely heat and cold, the one of 
which is assumed to have much more potency than the other, 
is not only opposed to the views entertained by physicists, but 
is also wholly irreconcilable with the ordinary principles of 
mechanics. But more than this, if we analyze the subject a 
little so as to remove some of the confusion of ideas which 
besets it, we shall find that these views are irreconcilable with 
even Dr. Carpenter's own explanation of the cause of the 
general oceanic circulation. 

Cold is not a something positive imparted to the polar waters 
giving them motion, and of which the tropical waters are 
deprived. If, dipping one hand into a basin filled with tropical 
water at 80^ and the other into one filled with polar water at 
32^, we refer to our sensations, we call the water in the one hot 
and that in the other cold ; but so far as the water itself is 
concerned heat and cold simply mean difference in the amoimts 
of heat possessed. Both the polar and the tropical water 
possess a certain amount of energy in the form of heat, only 
the polar water does not possess so much of it as the tropical. 

How, then, according to Dr. Carpenter, does polar cold im- 
part motion to the water P The warm water flowing in upon 
the polar column becomes chilled by cold, but it is not cooled 
below that of the water underneath ; for, according to Dr. Car- 
penter, the ocean in polar regions is as cold and as dense under- 
neath as at the surface. The cooled surface-water does not sink 
through the water underneath, like the surface-water of a pond 
chilled during a frosty night. ''The descending motion in 
column C wiU not consist," he says, " in a successional descent 
of surface-films from above downwards, but it will be a down- 
ward movement of the entire mass, as if water in a tall jar were 
being drawn off through an orifice at the bottom" (§ 29). 
There is a downward motion of the entire column, producing 
an outflow of water at the bottom towards the equatorial 
column W, which outflow is compensated by an inflow from 
the top of the equatorial column to the top of the polar column 
C. But what causes column C to descend ? The cause of the 



i8a CLIMATE AND TIME. 

descent is its excess of weight over that of column W. Column 
C descends and column AV asceudN, for the same reason that in 
a balance the heavy scale descends and the light scale rises. 
Column C 'descends not simply becaiise it is cold, but because it 
is colder than column "NV. Column C descends not simply 
because in consequence of being cold it is dense and therefore 
heavy, but because in consequence of being cold it is dcmer and 
therefore heavier than column AV. It might be as cold as frozen 
mercury and as heavy as lead ; but it would not on that account 
descend unless it were heavier tlian column W. ITie descent 
of column C and ascent of column "\V, and consequently the 
general oceanic circulation, results, therefore, according to Dr. 
Carpenter's explanation, from the difference in the weights of 
the two columns ; and the diilerence in the weiglits of the two 
columns results from their ditferenee of density : and the differ- 
ence of density of the two culumns in turn results from their 
difference of temporiituro. Dut it has already been proved that 
the difference of tonii)t'raturo between the polar and equatorial 
columns depends wholly on the ditllTence in the amount of heat 
received by each fnmi the sun. The equatorial column W pos- 
sesses more heat than the polar column C, solely because it 
receives more heat from the sun than column C. Consequently 
I)r. Carpenter's statement that the circulation is produced by 
jx>lar cold rather than by equatorial heat, is just as much in 
contradiction to his own theory as it is to the principles of 
nuvhaniis. Again, his admission that the general oceanic cir- 
culation '• cannot be pr^>duced by the application of heat to the 
surface/' is virtually a giving up the whole point in debate ; 
for according to his gravitation thcor\-, and every form of that 
theory, the circulation results from difference of temperature 
between equatorial and polar soas ; but this difference, as we 
have seen, is entirely owing to the difference in the amount of 
heat received finom the son at these two places. The heat re- 
oeited,lMyw)rrar,it *« Mizfiu»-lieat ; " for it is at the surface that the 

•U ita kaat from the sun ; and consequently if 

effect Teqaired, nothing else can. 




THE GRAVITATION THEORY, 183 

Jf. Duhuafs Experiments, — Refemtig to the experiments of 
M. Dubuat adduced by me to show that water would not run 
down a slope of 1 in 1,830,000,* he says, ** Xow the experi- 
ments of M. Dubuat had reference, not to the slow restoration 
of level produced by the motion of water on itself, but to the 
sensible movement of water flowing over solid surfaces and 
retarded by its friction against them " (S 22). Dr. Carpenter's 
meaning, I presume, is that if the incline consist of any solid 
substance, water will not flow down it ; but if it be made of 
water itself, icater will flow down it. But in il. Dubuat 's ex- 
periments it was only the molecules in actual contact with the 
solid incline that could possibly be retarded by friction against 
it. The molecules not in contact with the solid incline evidently 
rested upon an incline of icater, and were at perfect liberty to 
roll down that incline if thev chose : but they did not do so ; 
and consequently M. Dubuat's experiment proved that water 
will not flow over itself on an incline of 1 in 1,000,000. 

A, Begging of the Question at Ivsue. — " It is to be remem- 
bered," says Dr. Carpenter, " that, however small the original 
amount of movement may be, a momentum tending to its con- 
tinuance must be generated from the instant of its commence- 
ment ; so that if the initiating force be in constant action, 
there will be a progressive acceleration of its rate, until the 
increase of resistance equalises the tendency to further ac- 
celeration. Now, if it be admitted that the propagation of the 
diatorbance of equilibrium from one column to another is 
simply retarded^ not prevented, by the viscosity of the liquid, I 
cannot see how the conclusion can be resisted, that tho con- 
stantly maintained difference of gravity between the polar and 
equatorial columns really acts as a vis vira in maintaining a 
ciivnlation between them " (§ 35). 

If it be true, as Dr. Carpenter asserts, that in the case of 
the general oceanic circulation advocated by him " viscosity " 
rimplj rtiards motion, but does not prevent it, I certainly agree 
with him " that the constantly maintained difference of gravity 

•etotl ilope, lioweTer, doei not amount to more than 1 in 7,000,000. 



i84 CLIMATE AND TIME. 

between the polar and equatorial columns really acts as a 
tita in maintaining a circulation between them." But to 
assert that it merely retards, but does not prevent, motion, is 
simply begging the question at issue. It is an established prin- 
ciple that ii the force resisting motion be greater than the 
force tending to produce it, then no motion can take place and 
no work can be performed. The experiments of M. Dubuat 
prove that the force of the molecular resistance of water to 
motion is greater than the force derived from a slope of 1 in 
1,000,000; and therefore it is simply begging the question 
at issue to assert that it is less. The experiments of MM. 
Barlow, Bainey, and others, to which he alludes, are scarcely 
worthy of consideration in relation to the present question, 
because we know nothing whatever regarding the actual 
amoimt of force producing motion of the water in these experi- 
ments, further than that it must have been enormously greater 
than that derived from a slope of 1 in 1,000,000. 

Supposed Argument from the Tides, — Dr. Carpenter advances 
Mr. Ferrel's argument in regard to the tides. The power of 
the moon to disturb the earth's water, ho asserts, is, according 
to Herschel, only l-ll,400,000th part of gravity, and that of 
the sun not over l-25,736,400th part of gravity ; yet the 
moon's attractive force, even when coimteracted by the sun, 
will produce a rise of the ocean. But as the disturbance of 
gravity produced by difference of temperature is far greater 
than the above, it ought to produce circulation. 

It is here supposed that the force exerted by gravity on the 
ocean, resulting from difference of temperature, tending to 
produce the general oceanic circulation, is much greater than 
the force exerted on the ocean by the moon in the production 
of the tides. But if we examine the subject we shall find that 
the opposite is the case. The attraction of the moon tending 
to lift the waters of the ocean acts directly on every molecule 
from the surface to the bottom ; but the force of gravity tend- 
ing to produce the circulation in question acts directly on only 
a portion of the ocean. Gravity can exercise no direct foroA 



THE GRAVITATION THEORY. 185 

in impelling the underflow from the polar to the equatorial 
r^liona, nor in raising the water to the surface when it reaches 
the equatorial regions. Ch-avity can exercise no direct influ- 
ence in pulling the water horizontally along the earth's surface, 
nor in raising it up to the surface. The pull of gravity is 
always daumwardSf never horizontally nor upwards. Gravity 
will tend to pull the surface-water from the equator to the 
poles because here we have descent. Gravity will tend to sink 
the polar column because here also we have descent. But these 
are the only parts of the circuit where gravity has any tendency 
to produce motion. Motion in the other parts of the circuit, 
▼iz.y along the bottom of the ocean from the poles to the 
equator and in raising the equatorial column, is produced by 
the pressure of the polar column ; and consequently it is only 
indirectly that gravity may be said to produce motion in those 
parts. It is true that on certain portions of the ocean the 
force of gravity tending to produce motion is greater than the 
force of the moon's attraction, tending to produce the tides ; 
but this portion of the ocean is of inconsiderable extent. The 
total force of gravity acting on the entire ocean tending to 
produce circulation is in reality prodigiously less than the total 
force of the moon tending to produce the tides. 

It is no doubt a somewhat difficult problem to determine 
accurately the total amount of force exercised by gravity on 
the ocean ; but for our present purpose this is not necessary. 
All that we require at present is a very rough estimate indeed* 
And this can be attained by very simple considerations. Sup- 
pose we assume the mean depth of the sea to be, say, three 
nules. The mean depth may yet be foimd to be somewhat less 
than this, or it may be foimd to be somewhat greater ; a slight 
mistake, however, in regard to the mass of the ocean will not 
materially afiect our conclusions. Taking the depth at 3 miles, 
the force or direct pull of gravity on the entire waters of the 
ocean tending to the production of the general circulation will 
not amoimt to more than l-24,000,000,000th that of gravity, 
or only about l-2,100th that of the attraction of the moon in 



i86 CLIMATE AND TIME. 

the production of the tides. Let it be observed that I am 
referring to the force or pull of gravity, and not to hydrostatio 
pressure. 

The moon, by raising the waters of the ocean, will produce 
a slope of 2 feet in a quadrant ; and because the raised water 
sinks and the level is restored, Mr. Ferrel concludes that a 
similar slope of 2 feet produced by difference of temperature 
will therefore be sufficient to produce motion and restore leveL 
But it is overlooked that the restoration of level in the case of 
the tides is as truly the work of the moon as the disturbance 
of that level is. For the water raised by the attraction of the 
moon at one time is again, six hours afterwards, pulled down 
by the moon when the earth has turned round a quadrant. 

No doubt the earth's gravity alone would in course of time 
restore the level ; but this does not follow as a logical conse- 
quence from ilr. Ferrel's premises. If we suppose a slope to 
be produced in the ocean by the moon and the moon's attrac- 
tion withdrawn so as to allow the water to sink to its original 
level, the raised side will be the heaviest and the depressed 
side the lightest ; consequently the raised side will tend to sink 
and the depressed side mil tend to rise, in order that the ocean 
may regain its static equilibrium. But when a difference of 
level is produced by difference of temperature, the raised side 
is always the lightest and the depressed side is always the 
heaviest ; consequently the very effort which the ocean makes 
to maintain its equilibrium tends to prevent the level being 
restored. The moon produces the tides chiefly by means of a 
simple yielding of the entire ocean considered as a mass; 
whereas in the case of a general oceanic circulation the level is 
restored by a^tr of water at or near the surface. Consequently 
the amount of friction and molecular resistance to be overcome 
in the restoration of level in the latter case is much greater 
than in the former. The moon, as the researches of Sir 
William Thomson show, will produce a tide in a globe com- 
posed of a substance where no currents or general flow of the 
materials could possibly take place. 



THE GRAVITATION THEORY. 187 

Preuure as a Cause of Circubtion. — We sliall now briefly refer 
to the influence of pressure (the indirect effects of gravity) in 
the production of the circulation under consideration. That 
which causes the polar column C to descend and the equatorial 
column W to ascend, as has repeatedly been remarked, is the 
difference in the weight of the two columns. The efficient 
cause in the production of the movement is, properly speaking, 
gravity ; cold at the poles and heat at the equator, or, what is 
the same thing, the excess of heat received by the equator 
over that received by the poles is what maintains the differ- 
ence of temperature between the two columns, and conse- 
quently is that also which maintains the difference of weight 
between them. In other words, differeDce of temperature is the 
cause which maintains the state of disturbed equilibrium. But 
the efficient cause of the circulation in question is gravity. 
Gravity, however, could not act without this state of disturbed 
equilibrium; and difference of temperature may therefore be 
called, in relation to the circulation, a necessary condition, while 
gravity may be termed the cause. Gravity sinks column C 
directly y but it raises column W indirectly by means of pressure. 
The same holds true in regard to the motion of the bottom- 
waters from C to W, which is likewise due to pressure. The 
pressure of the excess of the weight of column C over that of 
column W impels the bottom-water equatorwards and lifts the 
equatorial column. But on this point I need not dwell, as I 
have in the preceding chapter entered into a full discussion as 
to how this takes place. 

We come now to the most important part of the inquiry, 
viz., how is the surface-water impelled from the equator to the 
poles ? Is pressure from behind the impelling force here as in 
the case of the bottom-water of the ocean P It seems to me 
that^ in attempting to account for the surface-flow from the 
equator to the poles, Dr. Carpenter's theory signally fails. The 
force to which he appeals appears to be wholly inadequate to 
produce the required effect. 

The experiments of M. Dabuat, as already noticed, prove that 



1 88 



CLIMATE AND TIME. 



any slope which can possibly result from the difference of tem- 
perature between the equator and the poles is wholly insufficient 
to enable gratity to move the waters ; but it does not neces- 
sarily prove that \!i[iq pressure resulting from the raised water at 
the equator may not be sufficient to produce motion. This 
point will be better understood from the following figure, where, 
as before, P represents the polar column and £ W the equa- 
torial column. 

Fig. 4. 




It will be observed that the water in that wedge-shaped 
portion TV C W forming the incline cannot be in a state of static 
equilibrium. A molecule of water at 0, for example, will be 
pressed more in the direction of C than in the direction of W, 
and the amount of this excess of pressure towards C will depend 
upon the height of W above the line C W. It is evident that 
the pressure tending to move the molecule at towards C will 
be far greater than the direct pull of gravity tending to draw a 
molecule at 0' lying on the surface of the incline towards C. 
The experiments of M. Dubuat prove that the direct force of 
gravity will not move the molecule at 0' — that is, cause it to 
roll down the incline W C ; but they do not prove that it may 
not yield to pressure from above, or that the pressure of the 
column W W will not move the molecule at 0. The pressure 
is caused by gravity, and cannot, of course, enable gravity to 
perform more work than what is derived from the energy of 
gravity ; it will enable gravity, however, to overcome resistance, 
which it could not do by direct action. But whether the 



THE GRAVITATION THEORY. 189 

preasnre remiltmg from the greater heiglit of the water at the 
equator due to its higher temperature be actually sufficient to 
produce displacement of the water is a question which I am 
wholly unable to answer. 

If we suppose 4 feet 6 inches to be the height of the equa- 
torial 8ur£EU)e above the polar required to make the two columns 
balance each other, the actual difference of level between the 
two columns will certainly not be more than one-half that 
amount, because, if a circulation exist, the weight of the polar 
column must always be in excess of that of the equatorial. But 
this excess can only be obtained at the expense of the surface- 
slope, as has already been shown at length. The surface-slope 
probably will not be more than 2 feet or 2 feet 6 inches. 
Suppose the ocean to be of equal density from the poles to the 
equator, and that by some means or other the surface of the 
ocean at the equator is raised, say, 2 feet above that of the 
poles, then there can be little doubt that in such a case the 
water would soon regain its level ; for the ocean at the equator 
being heavier than at the poles by the weight of a layer 2 
feet in thickness, it woidd sink at the former place and rise 
at the latter until equilibrium was restored, producing, of 
course, a very slight displacement of the bottom- waters towards 
the poles. It will be observed, however, that restoration of 
level in this case takes place by a simple yielding, as it were, 
of the entire mass of the ocean without displacement of the 
molecules of the water over each other to any great extent. In 
the case of a slope produced by difference of temperature, how- 
ever, the raised portion of the ocean is not heavier but lighter 
than the depressed portion, and consequently has no tendency 
to sink. Any movement which the ocean as a mass makes in 
order to regain equilibrium tends, as we have seen, rather to 
increase the difference of level than to reduce it. Restoration 
of level can only be produced by the forces which are in opera- 
tion in the wedge-shaped mass W C W, constituting the 
slope itself. But it will be observed by a glance at the Figure 
that, in order to the restoration of level, a large portion of 



igo 



CLIMATE AND TIME. 



the water W W at the equator will require to flow to 0, the 
pole. 

According to the general vertical oceanic circulation theory, 
pressure firom behind is not one of the forces employed in the 
production of the flow from the equator to the poles. This is 
evident ; for there can be no pressure from behind acting on 
the water if there be no slope existing between the equator and 
the poles. Dr. Carpenter not only denies the actual existence 
of a slope, but denies the necessity for its existence. But to 
deny the existence of a slope is to deny the existence of pros- 
sure, and to deny the necessity for a slope is to deny the neces- 
sity for pressure. That in Dr. Carpenter's theory the surface- 
water is supposed to be drawn from the equator to the poles, and 
not pressed forward by a force from behind, is further evident 
from the fact that he maintains that the force employed is not 
vis a tergo but vis a f route.* 

* IVoc of Boy. Q«og. 8oc., January 9, I87I9 f 29, 



CHAPTER XI. 

THB IXADEaUACT OP THE GRAVITATION THEORY PROVED BY 

ANOTHER METHOD. 

Qaaatity of Heat which can be conveyed by the General Oceanic Circolatioa 
trifling. — ^Tendcncy in the Advocates of the Graviuition Theory to under- 
Cfltinuite the Volume of the Gulf-Btream. — Volame of the Stream a0 deter- 
mined by the Cfiallen^fr. — Immense Volume of Warm Water discovered by 
Captain Nares. — Condition of North Atlantic inconsistent with the Gravita* 
tioQ Theory. — Dr. Carpenter's Estimate of the Thermal Work of the Gulf- 



I SHALL now proceed by another method to prove the in- 
adequacy of Buch a general oceanic circulation as that which 
Dr. Carpenter advocates. By contrasting the quantity of heat 
carried by the Gulf- stream from inter-tropical to temperate 
and polar regions with such amoimt as can possibly be con- 
veyed in the same direction by means of a general oceanic 
circulation, it will become evident that the latter sinks into 
utter insignificance before the former. 

In my earlier papers on the amount of heat conveyed by the 
Ghilf- stream,* I estimated the volume of that stream as equal to 
thai of a current 50 miles broad and 1,000 feet deep, flowing 
(from the surface to the bottom) at 4 miles an hour. Of course 
I did not mean, as Dr. Carpenter seems to suppose, that the 
stream at any particular place is 50 miles broad and 1,000 feet 
deep, or that it actually flows at the imiform rate of 4 miles an 
hour at surface and bottom. All I meant was, that the Gulf- 
stream is equal to that of a current of the above size and velocity. 
But in my recent papers on Ocean-currents, the substance of 
which appears in the present volume, to obviate any objections 

* Tram, of Geol. Soc. of Glasgow for April, 1S67 ; Phil. Uag. for June, 1867. 



192 CLIMATE AND TIME. 

on the grounds of having oyer-estimated the volume, I have 
taken that at one half this estimate, viz., equal to a current 50 
miles broad and 1,000 feet deep flowing at the rate of 2 milea 
an hour. I have estimated the mean temperature of the 
stream as it passes the Straits of Florida to be 65^, and have 
supposed that the water in its course become^ ultimately cooled 
down on an average to 40°. In this case each pound of water 
conveys 19,300 foot-pounds of heat from the Gulf of Mexico, 
to be employed in warming temperate and polar regions. 
Assuming these data to be correct, it follows that the amount 
of heat transferred from the Gulf of Mexico by this stream per 
day amounts to 77,479,650,000,000,000,000 foot-pounds. This 
enormous quantity of heat is equal to one-fourth of all that is 
received from the sun by the whole of the Atlantic Ocean from 
the Tropic of Cancer up to the Arctic Circle. 

This is the amount of heat conveyed from inter-tropical to 
temperate and polar regions by the Gulf-stream. What now 
is the amount conveyed by means of the General Oceanic Cir- 
culation ? 

According to this theory there ought to be as much warm 
water flowing from inter-tropical regions towards the Antarctic 
as towards the Arctic Circle. We may, therefore, in our calcu- 
lations, consider that the heat which is received in tropical 
regions to the south of the equator goes to warm the southern 
hemisphere, and that received on the north side of the equator 
to warm the northern hemisphere. The warm currents found 
in the North Atlantic in temperate regions we may conclude 
came from the regions lying to the north of the equator,— or, 
in other words, from that part of the Atlantic lying between 
the equator and the Tropic of Cancer. At least, according to 
the gravitation theory, we have no reason to believe that the 
quantity of warm water flowing from tropical to temperate and 
polar regions in the Atlantic is greater than the area between 
the equator and the Tropic of Cancer can supply — because it is 
affirmed that a very large proportion of the cold water found in 
the North. Atlantic comes, not from the arctic, but from the 




THE GRAVITATION THEORY. 193 

•ntaretic regions. But if the North Atlantic is cooled by a 
cold stream from the southern hemisphere, the southern hemi- 
sphere in turn must be heated by a warm current from the 
North Atlantic — ^unless we assume that the compensating cur- 
rent flowing from the Atlantic into the southern hemisphere is 
as cold as the antarctic current, which is very improbable. But 
Dr. Carpenter admits that the quantity of warm water flowing 
from the Atlantic in equatorial regions towards the south is 
even greater than that flowing northwards. '* The unrestricted 
communication/' he says, '' which exists between the antarctic 
area and the great Southern Ocean-basins would involve, if the 
doctrine of a general oceanic circulation be admitted, a much 
more considerable interchange of waters between the antarctic 
and the equatorial areas than is possible in the northern hemi- 
sphere."* 

We have already seen that, were it not for the great mass of 
warm water which finds its way to the polar regions, the tem- 
perature of these regions would be enormously lower than they 
really are. It has been shown likewise that the comparatively 
high temperature of north-western Europe is due to the same 
cause. But if it be doubtful whether the Gulf-stream reaches our 
shores, and if it be true that, even supposing it did, it " could 
only afiect the most superficial stratum," and that the great 
mess of warm water found by Dr. Carpenter in his dredging- 
expeditions came directly from the equatorial regions, and not 
from the Gulf-stream, then the principal part of the heating- 
effect must be attributed, not to the Gulf-stream, but to the 
general flow of water from the equatorial regions. It surely 
would not, then, be too much to assume that the quantity of 
heat conveyed from equatorial regions by this general flow of 
water into the North Atlantic is at least equal to that conveyed 
by the Gulf-stream. If we assume this to be the amount of 
heat conveyed by the two agencies into the Atlantic from inter- 
tropical regions, it wiU, of course, be equal to twice that con- 
veyed by the Gulf-stream alone. 

♦ Katur^t vol. i., p. 641. Proc Roy. Soc., vol. xviii., p. 478. 



194 CLIMATE AND TIME. 

We shall now consider whether the area of the Atlantic to 
the north of the equator is su£Scient to supply the amount of 
heat demanded by Dr. Carpenter s theory. 

The entire area of the Atlantic, extending from the equator 
to the Tropic of Cancer, including the Caribbean Sea and the 
Ghilf of Mexico, is about 7,700,000 square miles. 

The quantity of heat conveyed by the Oulf-stream through 
the Straits of Florida is, as we have already endeavoured to 
show, equal to all the heat received from the sun by 1,560,935 
square miles at the equator. The annual quantity of heat 
received from the sun by the torrid zone per unit surface, 
taking the mean of the whole zone, is to that received by the 
equator as 39 to 40, consequently the quantity of heat con- 
veyed by the Gulf-stream is equal to all the heat received by 
1,600,960 square miles of the Atlantic in the torrid zone. 

But if, according to Dr. Carpenter's views, the quantity of 
heat conveyed from the tropical regions is double that conveyed 
by the Ghilf-stream, the amount of heat in this case conveyed 
into the Atlantic in temperate regions will be equal to all 
the heat received from the sxm by 3,201,920 square miles of 
the Atlantic between the equator and the Tropic of Cancer. 
This is 32-77ths of all the heat received from the s\m by 
that area. 

Taking the annual quantity received per unit surface at the 
equator at 1,000, the quantities received by the three zf»ncs 
would be respectively as follows : — 

Equator 1000 

Torrid zone 975 

Temperate zodo 757 

Frigid zone . .... 454 

Now, if we remove from the Atlantic in tropical regions 
32-77th8 of the heat received from the sim, we remove 405 
parts from every 975 received from the sun, and consequently 
only 570 parts per unit surface remain. 

It has been shown* that the quantity of heat conveyed by 

* Chapter U. 



THE GRAVITATION THEORY. 195 

the Oulf-stream from the equatorial regions into the temperate 
regions is equal to 100-412ths of all the heat received by the 
Atlantic in temperate regions. But according to the theory 
under consideration the quantity removed is double this, or 
equal to 100-206ths of all the heat received from the sun. 
But the amount received from the sun is equal to 757 parts 
per unit surface ; add then to this 100'206ths of 757, or 367, 
and we have 1,124 parts of heat per unit surface as the amoimt 
possessed by the Atlantic in temperate regions. The Atlantic 
should in this case be much warmer in temperate than in 
tropical regions ; for in temperate regions it would possess 
1,124 parts of heat per unit surface, whereas in tropical regions 
it would possess only 570 parts per unit surface. Of course the 
heat conveyed from tropical regions does not all remain in 
temperate regions ; a very considerable portion of it must pass 
into the arctic regions. Let us, then, assume that one half 
goes to warm the Arctic Ocean, and the other half remains in 
the temperate regions. In this case 183 '5 parts would remain, 
and consequently 7574-183*5=940'5 parts would be the quan- 
tity possessed by the Atlantic in temperate regions, a quantity 
which still exceeds by no less than 370*5 parts the heat 
possessed by the Atlantic in tropical regions. 

As one half of the amount of heat conveyed from the tropical 
regions is assumed to go into the Arctic Ocean, the quantity 
passing into that ocean would therefore be equal to that which 
passes through the Straits of Florida, an amount which, as we 
have found, is equal to all the heat received from the sun by 
3,436,900 square miles of the Arctic Ocean.* The entire area 
covered by sea beyond the Arctic Circle is under 5,000,000 
square miles ; but taking the Arctic Ocean in round numbers 
at 5,000,000 square miles, the quantity of heat conveyed into 
it by currents to that received from the sun would therefore be 
as 3,436,900 to 5,000,000. 

The amount received on the unit surface of the arctic regions 
we have seen to be 454 parts. The amoimt received from the 

• Chapter II. 



£96 CLIMATE AND TIME. 

currents would therefore be 312 parts. This gives 766 parts of 
heat per unit surface as the quantity possessed by the Arctic 
Ocean. Thus the Arctic Ocean also would contain more heat 
than the Atlantic in tropical regions ; for the Atlantic in these 
regions would, in the case under consideration, possess only 570 
parts, while the Arctic Ocean would possess 766 parts. It is 
true that more rays are cut off in arctic regions than in 
tropical; but still, after making due allowance for this, the 
Arctic Ocean, if the theory we are considering were true, 
ought to be as warm as, if not warmer than, the Atlantic in 
tropical regions. The relative quantities of heat possessed by 
the three zones would therefore be as follows : — 

Atlantic, in torrid zone 670 

„ in temperate zone .... 940 
,, in fiigid zone • . . • • 766 

It is here assumed, however, that none of the heat possessed 
by the Gulf- stream is derived from the southern hemisphere, 
which, we know, is not the case. But supposing that as much 
as one half of the heat possessed by the stream came from the 
southern hemisphere, and that the other half was obtained 
from the seas lying between the equator and the Tropic of 
Cancer, the relative proportions of heat possessed by the three 
zones per given area would be as follows : — 

Atlantic, in torrid zone 671 

ill temperate zone . . . . 940 
in frigid zone 766 






This proves incontestably that, supposing there is such a 
general oceanic circulation as is maintained, the quantity of 
heat conveyed by means of it into the North Atlantic and 
Arctic Oceans must be trifling in comparison with that con- 
veyed by the Gulf-stream ; for if it nearly equalled that 
conveyed by the Gulf- stream, then not only the North Atlantic 
in temperate regions, but even the Arctic Ocean itself would 
be much warmer than the inter-tropical seas. In fact, so far as 
the distribution of heat over the globe is concerned, it is a 



THE GRAVITATION THEORY. 197 

matter of indifference whether there really is or is not such 
a thing as this general oceanic circulation. The enormous 
amount of heat conveyed by the Gulf-stream alone puts it 
beyond all doubt that ocean-currents are the great agents 
employed in distributing over the globe the excess of heat 
received by the sea in inter-tropical regions. 

It is therefore, so far as concerns the theory of a General 
Oceanic OirculatioD, of the utmost importance that the advo- 
cates of that theory should prove that I have over-estimated the 
thermal power of the Gulf-stream. This, however, can only 
be done by detecting some error either in my computation or 
in the data on which it is based ; yet neither Dr. Carpenter nor 
any one else, as far as I know, has challenged the accuracy of 
my figures. The question at issue is the correctness of the 
data ; but the only part of the data which can possibly admit 
of being questioned is my estimate of the volume and tempera- 
ture of the stream. Dr. Carpenter, however, does not maintain 
that I have over-estimated the temperature of the stream ; on 
the contrary, he affirms that I have really imder-estimated it. 
" If we assume," he remarks, " the limit of the stratum above 
60^ as that of the real Gulf-stream current, we shall find its 
average temperature to be somewhat higher than it has been 
stated by Mr. CroU, who seems to have taken 65^ as the average 
of the water flowing through the entire channel. The average 
surface temperature of the Florida channel for the whole year is 
80° ; and we may fairly set the average of the entire outgoing 
stream, down to the plane of 60°, at 70°, instead of 66° as 
estimated by Mr. Croll" (§ 141). It follows, then, that every 
pound of water of the Gulf-stream actually conveys 5 units of 
heat more than I have estimated it to do — the amount con- 
veyed being 30 units instead of 2o units as estimated by me. 
Consequently, if the Gulf-stream be equal to that of a current 
of merely 41 i miles broad and 1,000 feet deep, flowing at the 
rate of 2 miles an hour, it will still convey the estimated 
quantity of heat. But this estimate of the volume of the 
stream, let it be observed, barely exceeds one-third of that 



198 CLIMATE AND TIME. 

given by Herscliely Maury, and Colding,* and is little more 
than one-half that assigned to it by Mr. Laughton, while it very 
little exceeds that given by Mr. Findlay,t an author whom few 
will consider likely to overrate either the volume or heating- 
power of the stream. 

The important results obtained during the Challenger ex- 
pedition have clearly proved that I have neither over-estimated 
the temperature nor the volume of the Gulf-stream. Between 
Bermuda and Sandy Hook the stream is 60 miles broad and 
600 feet deep, with a maximimi velocity of from 3^ to 4 miles 
an hour. If the mean velocity of the entire section amounts to 
2^ miles an hour, which it probably does, the volimie of the 
stream must equal that given in my estimate. But we have 
no evidence that all the water flowing through the Straits of 
Florida passes through the section examined by the officers of 
the Challenger. Be this, however, as it may, the observations 
made between St. Thomas and Sandy Hook reveal the existence 
of an immense flow of warm water, 2,300 feet deep, entirely 
distinct from the water included in the above section of the 
Gulf-stream proper. As the thickest portion of this immense 
body of water joins the warm water of the Gulf- stream, Captain 
Nares considers that "it is evidently connected with it, and 
probably as an ofiFshoot." At Sandy Hook, according to him, 
it extends 1,200 feet deeper than the Gulf-stream itself, but off 
Charleston, 600 miles nearer the source, the same tempera- 
ture is found at the same depth. But whether it be an 
offshoot of the Gulf-stream or not, one thing is certain, it can 
only come from the Gulf of Mexico or from the Caribbean 
Sea. This mass of water, after flowing northwards for about 
1,000 miles, turns to the right and crosses the Atlantic in the 
direction of the Azores, where it appears to tliin out. 

If, therefore, we take into account tlie combined heat con- 

♦ Chapter ir. 

t Mr. Findiay considers that the daily discharge does not exceed 333 cuhio 
miles (Brit. A:js >c. Rep., 1869, p. 16i>). My eslimate makes it 378 cubic miles. 
Mr. Laughton's estimate is 630 cubic miles (Paper ** On Oce;in-cuiTciits," Journal 
ofR/jyal United-Service Institution, vol. xv.]. 



THE GRAVITATION THEORY. 199 

ivjed by both streams, my estimate of the heat traDsferred from 
inter-tropical regions into the North Atkntic will be found 
rather under than above the truth. 

lyr. Carpenter'9 Estimate of the Thermal Work of the Gulf' 
stream. — In the appendix to an elaborate memoir on Oceanic 
Circulation lately read before the Geographical Society, Dr. 
Carpenter endeavours to show that I have over-estimated the 
thermal work of the Gulf- stream. In that memoir* he has 
also favoured us with his own estimate of the Rectional area, 
rate of flow, and temperature of the stream. Even adopting 
his data, however, I find myself unable to arrive at his 
conclusions. 

Let us consider first his estimate of the sectional area of the 
stream. He admits that ''it is impossible, in the present state 
of our knowledge, to arrive at any exact estimate of the sectional 
area of the stream ; since it is for the most part only from the 
temperatures of its difEerent strata that we can judge whether 
they are, or are not, in movement, and what is the direction of 
their movement." Now it is perfectly evident that our esti- 
mate of the sectional area of the stream will depend upon what 
we assimie to be its bottom temperature. If, for example, we 
assume 70^ to be the bottom temperature, we shall have a small 
sectional area. Taking the temperature at 60^, the sectional 
area will be larger, and if 50° be assumed to be the temperature, 
the sectional area will be larger still, and so on. Now the 
small sectional area obtained by Dr. Carpenter arises from the 
fact of his having assumed the high temperature of 60° to be 
that of the bottom of the stream. He concludes that all the 
water below 60° has an inward flow, and that it is only that 
portion from 60° and upwards which constitutes the Gulf- 
stream. 1 have been unable to find any satisfactory evidence 
for assuming so high a temperature for the bottom of the 
stream. It must be observed that the water underlying the 
Gulf-stream is not the ordinary water of the Atlantic, but the 
cold current from the arctic regions. In fact, it is the same 

• Prooeedingo of the Royal Geographical Society, vol. xviii., p. 393. 
10 



aoo CLIMATE AND TIME. 

water wliicli reaches the equator at almost every point with a 
temperature not much above the freezing-point. It is therefore 
highly improbable that the under surface of the Gulf-stream 
has a temperature so high as 60^. 

Dr. Carpenter's method of measuring the mean velocity of 
the Ghilf-stream is equally objectionable. He takes the mean 
annual rate at the surface in the " Narrows '* to be two miles 
an hour and the rate at the bottom to be zero, and he concludes 
from this that the average rate of the whole is one mile an 
hour — the arithmetical mean between these two extremes. 
Now it will be observed that this conclusion only holds true on 
the supposition that the breadth of the stream is as great at 
the bottom as at the surface, which of course it is not. All 
admit that the sides of the Gulf-stream are not perpendicular, 
but slope somewhat in the manner of the banks of a river. 
The stream is broad at the surface and narrows towards the 
bottom. It is therefore evident that the upper half of the 
section has a much larger area than the lower ; the quantity of 
water flowing through the upper half with a greater velocity 
than one mile an hour must be much larger than the quantity 
flowing through the lower half with a less velocity than one 
mile an hour. 

His method of estimating the mean temperature of the stream 
is even more objectionable. He says, ** The average surface 
temperature of the Florida Channel for the whole year is 80°, 
and we may set the average of the entire outgoing stream 
down to the plane of 60° at 70°, instead of ^b^^ as estimated 
by Mr. Croll." If 80° be the surface and 60° be the bottom 
temperature, temperature and rate of velocity being assumed of 
course to decrease uniformly from the surface downwards, how 
is it possible that 70° can be the average temperature ? The 
amount of water flowing through the upper half of the section, 
with a temperature above 70°, is far more than the amount 
flowing through the under half of the section, with a tempera- 
ture below 70°. Supposing the lower half of the section to be 
as large as the upper half, which it is not, still the quantity of 



THE GRAVITATION THEORY, 201 

water flowing through it would only equal one-third of that 
flowing through the upper half, because the meun velocity of 
the water in the lower half would be only half a mile per hour, 
whereas the mean velocity of that in the upper half would be 
a mile and a half an hour. But the area of the lower half ia 
much less than that of the upper half, consequently the 
amount of water whose temperature is under 70^ must be 
even much under one-third of that, tlie temperature of which 
is above 70°. 

Had Dr. Carpenter taken the proper method of estimating 
the mean temperature, he would have found that 75°, even 
according to his own data, was much nearer the truth than 
70°. I pointed out, several years ago,* the fallacy of esti- 
mating the mean temperature of a stream in this way. 

So high a mean temperature as 75° for the Gulf-stream, 
even in the Florida Channel, is manifestly absurd, but if 60° 
be the bottom temperature of the stream, the mean tempera- 
ture cannot possibly be much under that amount. It is, of 
course, by under-estimating the sectional area of the stream 
that its mean temperature is over-estimated. We cannot 
reduce the mean temperature witliout increasing the sectional 
area. If my estimate of 65° be taken as the mean temperature, 
which I have little doubt will yet be found to be not far from 
the truth. Dr. Carpenter's estimate of the sectional area must 
be abandoned. For if 65° be the mean temperature of the 
stream, its bottom temperature must be far under 60°, and if 
the bottom temperature be much under 60°, then the sectional 
area must be greater than he estimates it to be. 

Be this, however, as it may ; even if we suppose that 60° 
will eventually be found to be the actual bottom temperature 
of the Gulf-stream, nevertheless, if the total quantity of heat 
conveyed by the stream from inter- tropical regions be estimated 
in the proper way, we shall still find that amount to be so 
enormous, that there is not sufficient heat remaining in thote 

• Phil. Mag. for October, 1871, p. 274. 



loa 



CLIMATE AND TIME. 



regions to supply Dr. Carpenter's oceanic circulation with a 
quantity as great for distribution in the North Atlantic. 

It therefore follows (and so far as regards the theory of 
Secular changes of climate, this is all that is worth contending 
for) that Ocean-currents and not a Gbneral Oceanic Circula- 
tion resulting firom gravity, are the great agents employed in 
the distribution of heat over the globe. 




CHAPTER Xn. 
MR. A. a. findlat's objections considered. 

Mr. Rndlay'fl E«tiniate of the Volame of the Oulf-stream. — Mean Temperatu* 
of a Croes Section less than Mean Temperature of Stream. — Reason of sooh 
DiTersitj of Opinion regarding Ocean-currents. — More rigid Method of 
InTestigation necessary. 

At the conclusion of the reading of Dr. Carpenter's paper 
before the Boyal Geographical Society, on January 9th, 1871, 
Mr. Findlay made the following remarks : — 

" When, by the direction of the United States Government, 
ten or eleven years ago, the narrowest part of the GKilf -stream 
was examined, figures were obtained which shut out all idea of 
its ever reaching our shores as a heat-bearing current. In the 
narrowest part, certainly not more than from 250 to 300 cubic 
miles of water pass per diem. Six months afterwards that 
water reaches the banks of Newfoundland, and nine or twelve 
months afterwards the coast of England, by which time it is 
popularly supposed to cover an area of 1,500,000 square miles. 
The proportion of the wat^r that passes through the Gulf of 
Florida will not make a layer of water more than 6 inches 
thick per diem over such a space. Every one knows how 
soon a cup of tea cools ; and yet it is commonly imagined that 
a film of only a few inches in depth, after the lapse of so long 
a time, has an eflect upon our climate. There is no need for 
calculations ; the thing is self-evident."* 

About five years ago, Mr. Findlay objected to the conclusicms 
which I had arrived at regarding the enormous heating-power 
of the Gulf-stream on the ground that I had over-estimated the 

* Proceedings of the Royal Geographical Society, vol. xv. 



104 CLIMATE AND TIME. 

volume of the stream. He stated that its yolume was only 
about the half of what I had estimated it to be. To obviate 
this objection, I subsequently reduced the volume to one-half 
of my former estimate.* But taking the volume at this low 
estimate, it was nevertheless found that the quantity of heat 
conveyed into the Atlantic through th<e Straits of Florida by 
means of the stream was equal to about one-fourth of all the 
heat received from the sun by the Atlantic from the latitude of 
the Strait of Florida up to the Arctic Circle. 

Mr. Findlay, in his paper read before the British Association, 
afiBrmed that the volume of the stream is somewhere from 294 
to 333 cubic miles per day ; but in his remarks at the close of 
Dr. Carpenter's address, he stated it to be not greater than 
from 250 to 300 cubic miles per day. I am unable to reconcile 
any of those figures with the data from which he appears to 
have derived them. In his paper to the British Association, 
he remarks that "the Gulf-stream at its outset is not more 
than 39 J miles wide, and 1,200 feet deep." " From all attain- 
able data, he computes the mean annual rate of motion to be 
65*4 miles per day ; but as the rate decreases with the depth, 
the mean velocity of the whole mass does not exceed 49*4 miles 
per day. When he speaks of the mean velocity of the Gulf- 
stream being so and so, he must refer to the mean velocity at 
some particular place. This is evident ; for the mean velocity 
entirely depends upon the sectional area of the stream. The 
place where the mean velocity is 49*4 miles per day must be 
the place where it is 39 J miles broad and 1,200 feet deep ; for 
he is here endeavouring to show us how small the volume of 
the stream actually is. Now, unless the mean velocity refers 
to the place where he gives us the breadth and depth of the 
stream, his figures have no bearing on the point in question. 
But a stream 39^ miles broad and 1,200 feet deep has a 
sectional area of 8*97 square miles, and this, with a mean 
velocity of 49*4 miles per day, will give 443 cubic miles of 
water. The amoimt, according to my estimate, is 459 cubic 

* Phil. Mag., Febniary, 1870. 




OBJECTIONS CONSIDERED. aos 

milefl per day ; it therefore exceeds Mr. Findlay's estimate by 
only 16 cubic miles. 

lilr. Findlay does not, as far as I know, consider that I have 
OTer*estimated the mean temperature of the stream. He states* 
that between Sand Key and Havanna the Gulf-stream is about 
1,200 feet deep, and that it does not reach the summit of a 
submarine ridge, which he states has a temperature of 60^. It 
is evident, then, that the bottom of the stream has a tempera- 
ture of at least 60°, which is within 5° of what I regard as the 
mean temperature of the mass. But the surface of the stream 
is at least 17° above this mean. Now, when we consider that 
it is at the upper ports of the stream, the place where the 
temperature is so much above 65°, that the motion is greatest, 
it is evident that the mean temperature of the entire moving 
mass must, according to Mr. Findlay, be considerably over 65°. 
It therefore follows, according to his own data, tliat the Gulf- 
stream conveys into the Atlantic an amount of heat equal 
to one-fourth of all the heat which the Atlantic, from the 
latitude of the Straits of Florida up to the arctic regions, 
derives from the sun. 

But it must be borne in mind that although the mean 
temperature of the cross section should be below 65°, it does 
not therefore follow that the mean temperature of the xcater 
flowing through this cross section must be below that temperature, 
for it is perfectly obvious that the mean temperature of the 
mass of water flowing through the cross section in a given time 
must be much higher than that of the cross section itself. The 
reason is very simple. It is in the upper half of the section 
where the high temperature exists ; but as the velocity of the 
stream is much greater in its upper than in its lower half, the 
greater portion of the water passing through this cross section 
is water of high temperature. 

But even supposing we were to halve Mr. Findlay 's own 
estimate, and assume that the volume of the stream is equal to 
only 222 cubic miles of water per day instead of 443, still the 

* Brit Amoc. Report, 1869, Sections, p. 160. 



io6 CLIMATE AND TIMK 

amount of heat conveyed would be equal to one*eighth part of 
the heat received from the sun by the Atlantic. But would 
not the withdrawal of an amount of heat equal to one-eighth of 
that received from the sun greatly affect the climate of the 
Atlantic P Supposing we take the mean temperature of the 
Atlantic at, say, 56°; this will make its temperature 295° 
above that of space. Extinguish the sun and stop the Ghilf- 
stream, and the temperature ought to sink 295°. How far, 
then, ought the temperature to sink, supposing the sun to 
remain and the Gulf-stream to stop ? Would not the with- 
drawal of the stream cause the temperature to sink some 30° P 
Of course, if the Gulf-stream were withdrawn and everything 
else were to remain the same, the temperature of the Atlantic 
would not actually remain 30° lower than at present ; for heat 
woidd flow in from all sides and partly make up for the loss of 
the stream. But nevertheless 30° represents the amount of 
temperature maintained by means of the heat from the stream. 
And this, be it observed, is taking the volume of the stream at 
a lower estimate than even Mr. Findlay himself would be 
willing to admit. Mr. Findlay says that, by the time the 
Gulf-stream reaches the shores of England, it is supposed to 
cover a space of 1,500,000 square miles. " The proportion of 
water that passes through the Straits of Florida will not 
make," according to him, " a layer of water more than 6 inches 
thick per diem over such a space." But a layer of water 
6 inches thick cooling 25° will give out 579,000 foot-pounds 
of heat per square foot. If, therefore, the Gulf-stream, as he 
asserts, supplies 6 inches per day to that area, then every 
square foot of the area gives off per day 579,000 foot-pounds 
of heat. The amount of heat received from the sun per square 
foot in latitude 55°, which is not much above the mean 
latitude of Great Britain, is 1,047,730 foot-pounds per day, 
taking, of course, the mean of the whole year ; consequently this 
layer of water gives out an amount of heat equal to more than 
one-half of all that is received from the sun. But assuming 
LO stream should leave the half of its heat on the 



t^^^e 



OBJECTIONS CONSIDERED. 207 

American shores and cariy to the shores of Britain only 
12|^ of heat, still we should have 289,500 foot-pounds per 
square foot, which notwithstanding %% more than equal to one- 
fourth 0/ that received from the sun. If an amount of heat so 
enormous cannot affect climate, what can ? 

I shall just allude to one other erroneous notion which pre- 
vails in regard to the Gulf-stream ; but it is an error which I 
by no means attribute either to Mr. Findlay or to Dr. Car- 
penter. The error to which I refer is that of supposing that 
when the Gulf-stream widens out to himdreds of miles, as it 
does before it reaches our shores, its depth must on this 
account be much less than when it issues from the Ghilf of 
Mexico. Although the stream may be hundreds of miles in 
breadth, there is no necessity why it should be only 6 inches, 
or 6 feet, or 60 feet, or even 600 feet in depth. It may just 
as likely be 6,000 feet deep as 6 inches. 

The Reason why such Dicersiiy of Opinion prevails in Regard 
to Ocean-currents. — In conclusion I venture to remark that 
more than nine-tenths of all the error and uncertainty which 
prevail, both in regard to the cause of ocean-currents and to 
their influence on climate, is due, not, as is generally supposed, 
to the intrinsic difficulties of the subject, but rather to the 
defective methods which have hitherto been employed in its 
investigation — that is, in not treating the subject according to 
the rigid methods adopted in other departments of physics. 
What I most particularly allude to is the disregard paid to the 
modem method of determining the amount of effects in absolute 
measure. 

But let me not be misunderstood on this point. I by no 
means suppose that the absolute quantity is the thing always 
required for its own sake. It is in most cases required simply 
as a means to an end ; and very often that end is the knowledge 
of the relative quantity. Take, for example, the Gulf-stream. 
Suppose the question is asked, to what extent does the heat 
conveyed by that stream influence the climate of the North 
Atlantic P In order to the proper answering of this question, 



fo8 CUM ATE AND TIME. 

tihe principal tUng required is to know what proportion the 
amount of heat conveyed by the stream into the Atlantic bears 
to that received from the sun by that area. We want the 
relaiive proportions of these two quantities. But how are we to 
obtain them? We can only do so by determining first the 
absolute quantity of each. We must first measure each before 
we can know how much the one is greater than the other, or, 
in other words, before we can know their relative proportions. 
We have the means of determining the absolute amount of heat 
received from the sun by a given area at any latitude with 
tolerable accuracy ; but the same cannot be done with equal 
accuracy in regard to the amount of heat conveyed by the Gidf- 
stream, because the volume and mean temperature of the stream 
are not known with certainty. Nevertheless we have sufficient 
data to enable us to fix upon such a maximum and minimum 
value to these quantities as will induce us to admit that the 
truth must lie somewhere between them. In order to give full 
justice to those who maintain that the Gulf-stream exercises 
but little influence on climate, and to put an end to all further 
objections as to the imcertainty of my data, I shall take a 
minimum to which none of them surely can reasonably object, 
viz. that the volume of the stream is not over 230 cubic miles 
per day, and the heat conveyed per poxmd of water not over 
124 units. Calculating from these data, we find that the 
amount of heat carried into the North Atlantic is equal to one- 
sixteenth of all the heat received from the sun by that area. 
There are, I presume, few who will not admit that the actual 
proportion is much higher than this, probably as high as 1 to 
3, or 1 to 4. But, who, without adopting the method I have 
pursued, could ever have come to the conclusion that the pro- 
portion was even 1 to 16 P He might have guessed it to be 
1 to 100 or 1 to 1000, but he never would have guessed it to be 
1 to 16. Hence the reason why the great influence of the Gulf- 
stream as a heating agent has been so much under-estimated. 
The same remarks apply to the gravitation theory of the 
enrrents. Viewed simply as a theory it looks very 




OBJECTIONS CONSIDERED. 



209 



xeaflonable. There is no one acquainted with physics but will 
admit that the tendency of the difTerence of temperature 
between the equator and the poles is to cause a surface-current 
from the equator towards the poles, and an under-current from 
the poles to the equator. But before we can prove that this 
tendency does actually produce such currents, another question 
must be settled, viz. is this force sufficiently great to produce 
the required motion? Now when we apply the method to 
which I refer, and determine the absolute amount of the force 
resulting from the difference of specific gravity, we discover 
that not to be the powerful agent which the advocates of the 
gravitation theory suppose, but a force so infinitesimal as not 
to be worthy of being taken into account when considering the 
oauaes by which currents are produced. 



CHAPTER Xin. 

THE WIND THEOBY OF OCEANIC CIBCULATIOK. 

Ooean-cnrrents not dae alone to the Trade-winds. — An Objection by yanry.— 
Trade- winds do not explain the Great Antarctic Current.— Ocean- cuirenta 
due to the System ot Winds. — The Syetem of Currents agrees with the 
System of the Winds. — Chart showing the Afi;Teemont between the System 
01 Currents and System of Winds. — Cause of the Qibraltar Current. — North 
Atlantic an immense Whirlpool. — Theory of Under Currents. — Difficulty 
regarding Under Currents obviated. — Work performed by the Wind in im- 
pelling the Water forward. — The ChaiUnger'a crucial Test of the Wind and 
Gravitation Theories. — North Atlantic above the Level ot Equator. — Thermal 
Condition of the Southern Ocean irreconcilable wiih the Gravitation Theory. 

Ocean-currents not due alone to the Trade-winds, — The 
generally received opinion amongst the advocates of the wind 
theory of oceanic circulation is that the Gnlf-stream and other 
currents of the ocean are due to the impulse of the trade-winds. 
The tendency of the trade-winds is to impel the inter-tropical 
waters along the line of the equator from east to west ; and 
were those regions not occupied in some places by land, this 
equatorial current would flow directly round the globe. Its 
westward progress, however, is arrested by the two great con- 
tinents, the old and the new. On approaching the land the 
current bifurcates, one portion trending northwards and the 
other southwards. The northern branch of the equatorial 
current of the Atlantic passes into the Caribbean Sea, and after 
making a circuit of the Gulf of Mexico, flows northward and 
continues its course into the Arctic Ocean. The southern 
branch, on the other hand, is deflected along the South- 
American coast, constituting what is known as the Brazilian 
current. In the Pacific a similar deflection occurs against the 
Afliatio coast, forming a current somewhat resembling the Gulf- 



THE WIND THEORY. tii 

Btream, a portion of whicli (Kamtschatka current) in like 
manner passes into the arctic regions. In reference to ab 
these various currents, the impelling cause is supposed to be 
the force of the trade-winds. 

It is, however, urged as an objection by Maury and other 
advocates of the gravitation theory, that a current like the 
Gulf-stream, extending as far as the arctic regions, could noV 
possibly be impelled and maintained by a force acting at the 
equatorial regions. But this is a somewhat weak objection. It 
seems to be based upon a misconception of the magnitude of the 
force in operation. It does not take into account that this force 
acts on nearly the whole area of the ocean in inter-tropical 
regions. If, in a basin of water, say three feet in diameter, a 
force is applied sufficient to produce a surface-flow one foot 
broad across the centre of the basin, the water impelled 
against the side will be deflected to the extremes of the vesseL 
And this result does not in any way depend upon the size of 
the basin. The same eflect which occurs in a small basin will 
occur in a large one, provided the proportion between the 
breadth of the belt of water put in motion and the size of the 
vessel be the same in both cases. It does not matter, therefore, 
whether the diameter of the basin be supposed to be three feet, 
or three thousand miles, or ten thousand miles. 

There \& a more formidable objection, however, to the theory. 
The trade- winds will account for the Gulf-stream, Brazil, Japan, 
Mozambique, and many other currents; but there are cur- 
rents, such as some of the polar currents, which cannot be so 
accounted for. Take, for example, the great antarctic current 
flowing northward into the Pacific. This current does not 
bend to the left under the influence of the earth's rotation and 
continue its course in a north-westerly direction, but actually 
bends round to the right and flows eastward against the South- 
American coast, in direct opposition both to the influence of 
rotation and to the trade- winds. The trade- wind theory, there- 
fore, is insufficient to account for all the facts. But there is 
yet another explanation, which satisfactorily solves our diffi- 



Ill CLIMATE AND TIME. 

eulties. The currents of tlie ocean owe their origin, not to the 
trade- winds alone, but to the prevailing winds of the globe 
(including, of course, the trade-winds). 

Ocean-currents due to the System of Winds. — If we leave out 
of account a few smaU inland sheets of water, the globe may be 
said to have but one sea, just as it possesses only one atmo* 
sphere. We have accustomed ourselves, however, to speak of 
parts or geographical divisions of the one great ocean, such as 
the Atlantic and the Pacific, as if they were so many separate 
oceans. And we have likewise come to regard the currents of 
the ocean as separate and independent of one another. This 
notion has no doubt to a considerable extent militated against 
the acceptance of the theory that the currents are caused by 
the winds, and not by difference of specific gravity ; for it leads 
to the conclusion that currents in a sea must flow in the direc- 
tion of the prevailing winds blowing over that particular sea. 
The proper view of the matter, as I hope to be able to show, is 
that which regards the various currents merely as members of 
one grand system of circulation produced, not by the trade- 
winds alone, nor by the prevailing winds proper alone, but by 
the combined action of all the prevailing winds of the globe, 
regarded as one system of circulation. 

If the winds be the impelling cause of currents, the direction 
of the currents will depend upon two circumstances, viz. : — 
(1) the direction of the prevailing winds of the globe, including, 
of course, under this term the prevailing winds proper and the 
trade- winds; and (2) the conformation of land and sea. It 
follows, therefore, that as a current in any given sea is but a 
member of a general system of circulation, its direction is deter- 
mined, not alone by the prevailing winds blowing over the sea 
in question, but by the general system of prevailing winds. It 
may consequently sometimes happen that the general system 
of winds may produce a current directly opposite to the pre- 
vailing wind blowing over the current. The accompanying 
Chart (Plate I.) shows how exactly the system of ocean-cur- 
lesk^umeA with the system of the prevailing winds. The fine 




THE WIND THEORY. ti5 

lines indicate the paths of the prevailing winds, and the fine 
arrows the direction in which the wind blows along those 
paths. The large arrows show the direction of the principal 
ocean-currents. 

The directions and paths of the prevailing winds have been 
taken from Messrs. Johnston's small physical Atlas, which, I 
find, agrees exactly with the direction of the prevailing winds 
as deduced from the four quarterly wind charts lately published 
by the Hydrographic Department of the Admiralty. The 
direction of the ocean-currents has been taken from the Current- 
chart published by the Admiralty. 

In every case, without exception, the direction of the main 
currents of the globe agrees exactly with the direction of the 
prevailing winds. There could not possibly be a more con- 
vincing proof that those winds are the cause of the ocean- 
currents than this general agreement of the two systems as 
indicated by the chart. Take, for example, the North Atlantic. 
The Gulf- stream follows exactly the path of the prevailing 
winds. The Gulf- stream bifurcates in mid- Atlantic ; so does 
the wind. The left branch of the stream passes north-eastwards 
into the arctic regions, and the right branch south-eastwards 
by the Azores ; so does the wind. The south-eastern branch of 
the stream, after passing the Canaries, re-enters the equatorial 
current and flows into the Gulf of Mexico ; 4he same, it will be 
observed, holds true of the wind. A like remarkable agree- 
ment exists in reference to all the other leading currents of the 
ocean. This is particularly seen in the case of the great ant- 
arctic current between long. 140° W. and 160° W. This current, 
flowing northwards from the antarctic regions, instead of 
bending to the left under the influence of rotation, turns to the 
right when it enters the regions of the westerly winds, and 
flows eastwards towards the South- American shores. In fact, 
all the currents in this region of strong westerly winds flow in 
an easterly or north-easterly direction. 

Taking into account the eflects resulting from the conforma- 
tion of sea and land, the system of ocean-currents agreei 



"4 CLIMATE AND TIME. 

predsely with tlie system of the winds. All the principal 
currents of the globe are in fact moving in the exact direction 
in which they ought to move, assuming the winds to be the 
sole impelling cause. In short, so perfect is the agreement 
between the two systems, that, given the system of winds and 
the conformation of sea and land, and the direction of all the 
currents of the ocean, or more properly the system of oceanic 
circulation, might be determined d, priori. Or given the 
system of the ocean-currents together with the conformation of 
sea and land, and the direction of the prevailing winds could 
also be determined d priori. Or, thirdly, given the system of 
winds and the system of currents, and the conformation of sea 
and land might be roughly determined. For example, it can 
be shown by this means that the antarctic regions are probably 
occcupied by a continent and not by a number of separate 
islands, nor by sea. 

While holding that the currents of the ocean form one 
system of circulation, we must not be supposed to mean that 
the various currents are connected end to end, having the same 
water flowing through them all in succession like that in a 
heating-apparatus. All that is maintained is simply this, that 
the currents are so mutually related that any great change in 
one would modify the conditions of all the others. For ex- 
ample, a great increase or decrease in the easterly flow of 
antarctic water in the Southern Ocean would decrease or 
increase, as the case might be, the strength of the West 
Australian current ; and this change would modify the equa- 
torial current of the Indian Ocean, a modification which in 
like manner would affect the Agulhas current and the Southern 
Atlantic current — this last leading in turn to a modification of 
the equatorial current of the Atlantic, and consequently of the 
Brazilian current and the Oulf-stream. Furthermore, since 
a current impelled by the winds, as Mr. Laughton in his 
excellent paper on Ocean-currents justly remarks, tends to 
leave a vacancy benind, it follows that a decrease or increase 
in the Gulf-stream would affect the equatorial current, the 



THE WIND THEORY. tis 

Agulhas current, and all the other currents back to the 
antarctic currents. Again, a large modification in the great 
antarctic drift-current would in like manner affect all the 
currents of the Pacific. On the other hand, any great change 
in the currents of the Pacific would ultimately affect the 
currents of the Atlantic and Indian Oceans, through its in- 
fluence on the Cape Horn current, the South Australian 
current, and the current passing through the Asiatic archi- 
pelago; and vice versd, any changes in the currents of the 
Atlantic or Indian Oceans would modify the currents of the 
Pacific. 

Cause of Oibraltar Current. — I may now consider the cause 
of the Gibraltar current. There can be little doubt that this 
current owes its origin (as Mr. Laughton points out) to the 
Oulf-stream. " I conceive/' that author remarks, " that the 
Gibraltar current is distinctly a stream formed by easterly drift 
of the North Atlantic, which, although it forms a southerly 
current on the coast of Portugal, is still strongly pressed to 
the eastward and seeks the first escape it can find. So great 
indeed does this pressure seem to be, that more water is forced 
through the Straits than the Mediterranean can receive, and 
a part of it is ejected in reverse currents, some as lateral 
currents on the surface, some, it appears, as an under current 
at a considerable depth."* The funnel-shaped nature of the 
strait through which the water is impelled helps to explain 
the existence of the under current. The water being pressed 
into the narrow neck of the channel tends to produce a 
slight banking up ; and as the pressure urging the water 
forward is greatest at the surface and diminishes rapidly 
downwards, the tendency to the restoration of level will cause 
an underflow towards the Atlantic, because below the surface 
the water will find the path of least resistance. It is evident 
indeed that this underflow will not take place toward the 
Mediterranean, from the fact that that sea is already filled to 
overflowing by the current received from the outside ocean. 

• Journal of Royal United-Serrice Institute, vol. xv. 



ii6 CLIMATE AND TIME. 

I£ we examine the Current-chart published by the Hydro- 
graphic Department of the Admiralty, we shall find the 
Gibraltar current represented as merely a continuation of the 
S.E. flow of Oulf-stream water. Now, if the arrows shown 
upon this chart indicate correctly the direction of the flow, we 
must become convinced that the Gulf-stream water cannot 
possibly avoid passing through the Gibraltar Strait. Of course 
the excess of evaporation over that of precipitation within the 
Mediterranean area would alone suffice to produce a consider- 
able current through the Strait ; but this of itself would not 
fill that inland sea to overflowing.* 

The Atlantic may, in fact, be regarded as an immense whirl- 
pool with the Saragossa Sea as its vortex ; and although it is 
true, as will be seen from an inspection of the Chart, that the 
wind blows round the Atlantic along the very path taken by 
the water, impelling the water forward along every inch of its 
course, yet nevertheless it must hold equally true that the 
water has a tendency to flow ofi* in a straight line at a tangent 
to the circular course in which it is moving. But the water is 
BO hemmed in on all sides that it cannot leave this circular 
path except only at two points ; and at these two points it 
actually does flow outwards. On the east and west sides the 
land prevents any such outflow. Similarly, in the south the 
escape of the water is frustrated by the pressure of the opposing 
currents flowing from that quarter ; while in the north it is 
prevented by the pressure exerted by polar currents from Davis 
Strait and the Arctic Ocean. But in the Strait of Gibraltar 
and in the north-eastern portion of the Atlantic between 

• Dr. Carpenter (Proc. of Roy. Gcog. Soc., vol. xviii., p. 334) misapprehends 
me in supposing that I attribute the Gibraltar current wholly to the (xnlf- 
Btream. In the very page from which he derives or could derive his opinion as 
to my views on the subject (Phil. Mag. for March, 1874, p. 182), I distinctly 
state that "the excess of evaporation over that of precipitation within the Medi- 
terranean area would of itself produce a considerable current through the Strait.'* 
That the Gibraltar current is due to two causes, (1) the pressure of the Gulf- 
•trcam, and (2) excess of evaporation over precipitation in the Mediterranean, has 
always appeared to me so perfectly obvious, that I never hold nor could have 
held any other opinion on the subject. 



THE WIND THEORY. ji; 

Iceland and the north-eastom shores of Europe there is no 
resistance offered: and at these two points an outflow does 
actually take place. In both cases, however, especially the 
latter, the outflow is greatly aided by the impulse of the 
prevailing winds. 

No one, who will glance at the accompanying chart (Plate I.) 
showing how the north-eastern branch of the Gulf-stream 
bends round and, of course, necessarily presses against the 
coast, can fail to understand how the Atlantic water should be 
impelled into the Gibraltar Strait, even although the loss 
fustained by the Mediterranean from evaporation did not 
exceed the gain from rain and rivers. 

Theory of Under Currents, — The consideration that ocean- 
currents are simply parts of a system of circulation produced 
by the system of prevailing winds, and not by the impulse 
of the trade- winds alone, helps to remove the difiiculty which 
some have in accounting for the existence of under- currents 
without referring them to difierence of specific gravity. 
Take the case of the Gulf-stream, which passes under the 
polar stream on the west of Spitzbergen, this latter stream 
passing in turn under the Gulf-stream a little beyond Bear 
Island. The polar streams have their origin in the region 
of prevailing northerly winds, which no doubt extends to 
the pole. The current flowing past the western shores of 
Spitzbergen, throughout its entire course up to near the 
point where it disappears imder the warm waters of the 
Gulf-stream, lies in the region of these same northerly winds. 
Now why should this current cease to be a surface current as 
soon as it passes out of the region of northerly into that of 
south-westerly winds? The explanation seems to be this: 
when the stream enters the region of prevailing south-westerly 
winds, its progress southwards along the surface of the ocean is 
retarded both by the wind and by the surface water moving in 
opposition to its course ; but being continually pressed forward 
by the impulse of the northerly winds acting along its whole 
course back almost to the pole, perhaps, or as far north at leasl 



ii8 CLIMATE AND TIME. 

as tlie sea is not wholly covered with ice, the polar current 
cannot stop when it enters the region of opposing winds and 
currents ; it must move forward. But the water thus pressed 
from behind will naturally take the path of least resistance. 
Now in the present case this path will necessarily lie at a 
considerable distance below the surface. Had the polar stream 
simply to contend with the Oulf-stream flowing in the opposite 
direction, it would probably keep the surface and continue its 
course along the side of that stream ; but it is opposed by the 
winds, from which it cannot escape except by dipping down 
under the surface ; and the depth to which it will descend will 
depend upon the depth of the surface current flowing in the 
opposite direction. There is no necessity for supposing a 
heaping up of the water in order to produce by pressure a 
force sufficient to impel the under current. The pressure of 
the water from behind is of itself enough. Tho same explana- 
tion, of course, applies to the case of the Gulf-stream passing 
under the polar stream. And if we reflect that these under 
currents are but parts of the general system of circulation, and 
that in most cases they are currents compensating for water 
drained off at some other quarter, we need not wonder at the 
distance which they may in some cases flow, as, for example, 
from the banks of Newfoundland to the Gulf of Mexico. The 
under currents of the Gulf-stream are necessary to compensate 
for the water impelled southwards by the northerly winds ; and 
again, the polar under currents are necessary to compensate for 
the water impelled northward by the south and south-westerly 
winds. 

But it may be asked, how do the opposing currents succeed 
in crossing each other? It is evident that the Gulf-stream 
must plunge through the whole thickness of the polar stream 
before it can become an under current, and so likewise must 
the cold water of the polar-flow pass through the genial water 
of the Gulf-stream in order to get underneath it and continue 
on its course towards the south. The accompanying diagram 
(Plate II., Fig. 1) will render this sufficiently intelligible. 



THE WIND THEORY. 219 

Now these two great ocean-currents are so compelled to 
interaect each other for the simple reason that they cannot turn 
aside, the one to the left and the other to the right. When 
two broad streams like those in question are pressed up against 
each other, they succeed in mutually intersecting each other's 
path by breaking up into bands or belts — the cold water being 
invaded and pierced as it were by long tongues of warm water, 
while at the same time the latter is similarly intersected by 
corresponding protrusions of cold water. The two streams 
become in a manner interlocked, and the one passes through 
the other very much as we pass the fingers of one hand between 
the fingers of the other. The diagram (Plate II., Fig. 2), 
representing the surface of the ocean at the place of meeting 
of two opposing currents, will show this better than description. 
At the surface the bands necessarily assume the tongue-shaped 
appearance represented in the diagram, but when they haye 
succeeded in mutually passing down through the whole thick- 
ness of the opposing currents, they then unite and form two 
definite under currents, flowing in opposite directions. The 
polar bands, after penetrating the Giilf-strcam, unite below to 
form a southward-flowing under current, and in the same way 
the Gulf-stream bands, uniting underneath the polar current, 
continue in their northerly course as a broad under current of 
warm water. That this is a correct representation of what 
actually occurs in nature becomes evident from an inspection 
of the current charts. Thus in the chart of the North Atlantic 
which accompanies Dr. Petermann's Memoir on the Gulf-stream, 
we observe that south of Spitzbergcn the polar current and 
the Gulf-stream are mutually interpenetrated — long tongues 
invading and dipping down underneath the Gulf- stream, while 
in like manner the polar current becomes similarly intersected 
by well-marked protrusions of warm water flowing from the 
south. (See Plate II., Fig. 3.) 

No accurate observations, as far as I know, have been made 
regarding the amount of work performed by the wind in im- 
pelling the water forward ; but when we consider the great 



no CLIMATE AND TIME. 

retarding effect of objects on the earth's Bnrface, it is quite 
apparent that the amount of work performed on the surface of 
the ocean must be far greater than is generally supposed. For 
example, Mr. Buchan, Secretary to the Scottish Meteorological 
Society, has shown * that a fence made of slabs of wood three 
inches in width and three inches apart from each other is a 
protection even during high winds to objects on the lee side 
of it, and that a wire screen with meshes about an inch apart 
affords protection during a gale to flower-pots. The same 
writer was informed by Mr. Addie that such a screen put up at 
Bockville was torn to pieces by a storm of wind, the wire screen 
giving way much in the same way as sails during a hurricane 
at sea. 

The " Challenger's " Cmcial Test of the Wind and Gravitation 
Theories of Oceanic Circulation. — It has been shown in former 
chapters that all the facts which have been adduced in support 
of the gravitation theory are equally well explained by the 
wind theory. We may now consider a class of facts which do 
not appear to harmonize with both theories. The recent 
investigations of the Challenger Expedition into the thermal 
state of the ocean reveal a condition of things which appears to 
me utterly irreconcilable with the gravitation theory. 

It is a condition absolutely essential to the gravitation theory 
that the surface of the ocean should be highest in equatorial 
regions and slope downwards to either polo. Were water 
absolutely frictionless, an incline, however small, would be 
sufficient to produce a surface-flow from the equator to the 
poles, but to induce such an effect some slope there must be, 
or gravitation could exercise no power in drawing the surface- 
water polewards. 

The researches of the Challenger Expedition bring to light 
the striking and important fact that the general surface of the 
North Atlantic in order to produce equilibrium must stand at a 
higher level than at the equator. In other words the surface of 

* rai>er read to the Edinburgh Botanical Society on January 8, 1874. 



THE WIND THEORY. 221 

the Atlantic is lowest at tlie equator, and rises with a gentle slope 
to well nigh the latitude of England. If this be the case, then 
it is mechanically impossible that, as far as the North Atlantic 
is concerned, there can be any such general movement as Dr. 
Carpenter believes. Gravitation can no more cause the surface- 
water of the Atlantic to flow towards the arctic regions than it 
can compel the waters of the Gulf of Mexico up the Mississippi 
into the Missouri. The impossibility is equally great in both 



In order to prove what has been stated, let us take a section 
of the mid- Atlantic, north and soutb, across the equator ; and, 
to give the gravitation theory every advantage, let us select 
that particular section adopted by Dr. Carpenter as the one of 
all others most favourable to his theory, viz.. Section marked 
No. VIII. in his memoir lately read before the Royal Geo« 
graphical Society.* 

The fact that the polar cold water comes so near the surface at 
the equator is regarded by Dr. Carpenter as evidence in favour 
of the gravitation theory. On first looking at Dr. Carpenter's 
section it forcibly struck me that if it was accurately drawn, the 
ocean to be in equilibrium would require to stand at a higher 
level in the North Atlantic than at the equator. In order, 
therefore, to determine whether this is the case or not I asked 
the hydrographer of the Admiralty to favour me with the tem- 
perature soundings indicated in the section, a favour which was 
most obligingly granted. The following are the temperature 
soundings at the three stations A, B, and C. The temperatures 
of C are the mean of six soundings taken along near the 
equator : — 

• Pr »^. R'.y. Geog. Soc, vol. xviii., p. 362. A more advantageous section 
might have been chuttt^n, but this wiU suffice. The section referred to is shown 
in PJate III. The pociUiarity of this section, as will be observed, is the thin- 
ness of the warm strata at the equator, ai compared with that of the heated 
«mter in the North Atlantic. 



121 



CLIMATE AND TIME. 





• A 


B 


C 
ICeeaofeix 


Depth 


LatSTM'N. 


LatsriCN. 


temperature soond- 


Iftthoma. 


Long. 41" 44' W. 


Long.88<'4JrW. 


inga near equator. 


Temperature. 


Temperature. 


Depth in 
Fathoms. 


Tempera- 
ture. 


Surface. 


70°0 


72*0 


Surface. 


77-9 


100 


63-6 


67-0 


10 


77-2 


200 


60-6 


67-6 


20 


771 


300 


600 


625 


30 


76-9 


400 


64-8 


47-7 


40 


71-7 


600 


46-7 


43-7 


60 


640 


600 


41-6 


41-7 


60 


60-4 


700 


40-6 


40-6 


70 


69-4 


800 


381 


39-4 


80 


68-0 


900 


37-8 


39-2 


90 


680 


1000 


37-9 


38-3 


100 


66-6 


1100 


37-1 


380 


160 


510 


1200 


87-1 


37-6 


200 


46-6 


1300 


37-2 


36-7 


300 


42-2 


1400 


871 


36-9 


400 


40-3 


1600 


• • 


86-7 


600 


38-9 


2700 


35-2 


• • 


600 


39-2 


2720 


. • 


35*4 


700 
800 
900 
1000 
1100 
1200 
1300 
1400 
1600 

Bottom. 

1 


.390 
391 
38-2 
369 
37-6 
36-7 
36-8 
3<)-4 
3() 1 
3i-7 
1 



On computing the extent to which the three columns A, B, 
and C are each expanded by heat according to Muncke's table 
of the expansion of sea water for every degree Fahrenheit, I 
found that column B, in order to be in equilibrium with C (the 
equatorial column), would require to have its surface standing 
fidly 2 feet 6 inches above the level of column C, and column A 
fully 3 feet 6 inches above that column. In short, it is evident 
that there must be a gradual rise from the equator to latitude 
38° N. of 3^ feet. Any one can verify the accuracy of these 
results by making the necessary computations for himself.* 

* The temperature of column C in Dr. Carpenter's section is somcwliat less 



THE WIND THEORY. 223 

I may observe that, had column C extended to the same 
depth as columns A and B, the difference of level would be 
considerably greater, for column C requires to balance only that 
portion of columns A and B which lies above the level of its 
base. Suppose a depth of ocean equal to that of column C to 
extend to the north pole, and the polar water to have a uniform 
temperature of 32° from the surface to the bottom, then, in order 
to produce equilibrium, the surface of the ocean at the equator 
would require to be 4 feet 6 inches above that at the pole. 
But the surface of the ocean at B would be 7 feet, and at 
A 8 feet, above the poles. Gravitation never could have caused 
the ocean to assume this form. It is impossible that this 
immense mass of warm water, extending to such a depth in the 
North Atlantic, could have been brought from equatorial 
regions by means of gravitation. And, even if we suppose this 
accumulation of warm water can be accoimted for by some 
other means, still its presence precludes the possibility of any 
such surface- flow as that advocated by Dr. Carpenter. For so 
long as the North Atlantic stands 3^ feet above the level of the 
equator, gravitation can never move the equatorial waters pole- 
wards. 

There is another feature of this section irreconcilable with 
the gravitation theory. It will be observed that the accumula- 
tion of warm water is all in the North Atlantic, and that there 
is little or none in the south. But according to the gravitation 
theory it ought to have been the reverse. For owing to the 
unrestricted communication between the equatorial and antarctic 
regions, the general flow of water towards the south pole is, 
according to that theory, supposed to be greater than towards 
the north, and consequently the quantity of warm equatorial 
water in the South Atlantic ought also to be greater. Dr. 
Carpenter himself seems to be aware of this difficulty besetting 
the theory, and meets it by stating that " the upper stratum of 

than that given in the foregoing table ; so that, according to that section, the 
dilferonco of level boLween colimrn C and columns A and B would be gieater 
thitn my estimate. 

11 



214 CLIMATE AND TIME. 

the North Atlantio is not nearly as mucli cooled down by its 
limited polar underflow, as that of the South Atlantic is by the 
▼ast movement of antarctic water which is constantly taking 
place towards the equator/' But this ''vast movement of 
antarctic water " necessarily implies a vast counter-movement 
of warm surface-water. So that if there is more polar water in 
the South Atlantio to produce the cooling effect, there shoidd 
likewise be more warm water to be cooled. 

According to the wind theory of oceanic circulation the 
explanation of the whole phenomena is simple and obvious. It 
has already been shown that owing to the fact that the S. E. 
trades are stronger than the N. E., and blow constantly over 
upon the northern hemisphere, the warm surface-water of the 
South Atlantic is drifted across the equator. It is then carried 
by the equatorial current into the Gulf of Mexico, and after- 
wards of course forms a part of the Ghilf-stream. 

The North Atlantic, on the other hand, not only does not 
lose its surface heat like the equatorial and South Atlantic, but 
it receives from the Ghilf-stream in the form of warm water an 
amount of heat, as we have seen, equal to one-fourth of all the 
heat which it receives from the sun. The reason why the 
warm surface strata are so much thicker on the North Atlantic 
than on the equatorial regions is perfectly obvious. The surface- 
water at the equator is swept into the Gulf of Mexico by the 
trade winds and the equatorial current, as rapidly as it is 
heated by the sun, so that it has not time to gather to any 
great depth. But all this warm water is carried by the Gulf- 
stream into the North Atlantic, where it accumulates. That 
this great depth of warm water in the North Atlantic, repre- 
sented in the section, is derived from the Gulf-stream, and not 
from a direct flow from the equator due to gravitation, is 
further evident from the fact that temperature soimding A in 
latitude 38° N. is made through that immense body of warm 
water, upwards of 300 fathoms thick, extending from Bermuda 
^^^tf the Azores, discovered by the Challenger Expedition, 
^■^^^Hfar regarded by Captain Nares as an offshoot of the 



THE WIND THEORY, 225 

Qulf-stream. This, in Captain Nares's Report, is No. 8 " tern 
perature sounding/' between Bermuda and the Azores ; sound- 
ing B is No. 6 " temperature curve," between Teneriflfe and St. 
Thomas. 

There is an additional reason to the one already stated why 
rhe surface temperature of the South Atlantic should be so 
much below that of the North. It is perfectly true that what- 
ever amount of water is transferred from the southern hemi- 
sphere to the northern must be compensated by an equal 
amount from the northern to the southern hemisphere, never- 
theless the warm water which is carried off the South Atlantic 
by the winds is not directly compensated by water from the 
north, but by that cold antarctic current whose exi«tence is so 
well known to mariners from the immense masses of ice which 
it brings from the Southern Ocean. 

Thermal Condition 0/ Southern Ocean.— ^The thermal condition 
of the Southern Ocean, as ascertained by the Challenger Expe- 
dition, appears to me to be also irreconcilable with the gravita- 
tion theory. Between the parallels of latitude 65° 42' S. and 
50° 1' S., the ocean, with the exception of a thin stratum at the 
surface heated by the sun's rays, was found, down to the depth 
of about 200 fathoms, to be several degrees colder than the 
water underneath.* The cold upper stratum is evidently an 
antarctic current, and the warm underlying water an equatorial 
under current. But, according to the gravitation theory, the 
colder water should be underneath. 

The very fact of a mass of water, 200 fathoms deep and 
extending over fifteen degrees of latitude, remaining above 
water of three or four degrees higher temperature shows how 
little influence difl'erenoe of temperature has in producing 
motion. If it had the potency which some attribute to it, one 
would suppose tliat tliis cold stratum should sink down and 
displace the warm water underneath. If difference of density 
is sufficient to move the water horizontally, surely it must be 
more than sufficient to cause it to sink vertically. 

* Cuptain Nares's Report, July 30, 1374. 



CHAPTER XIV. 

THE WIND THEORY OF OCEANIC CIRCULATION IN RELATION TO 

CHANGE OF CLIMATE 

Direciioii of CurrenU depends on Direction of the Winds. — Causes which affect 
the Dir^ciion uf Currents will affect Climate. — How Change of Eccentricity 
atiects the Mode of Distrihntion of the Winds. — Mutual Reaction of Cause 
and Effect. — Displacement of the Great Equatorial Current. — Displacement 
of the Median Line between the Trades, and its Effect on Currents. — Ocean- 
currents in Relation to the Distribution of Plants and Animals. — Alternate 
Cold and Warm Periods in North and South. — Mr. Darwin's Views quoted. 
— How Glaciers at the Equator may be accounted for. — Migration across the 
Equat<jr. 

Oceari'Currcnh in Relation to Change of Climate, — In my 
attempts to prove that oceanic circulation is produced by the 
winds and not by diflFerence of specific gravity, and that ocean- 
currents are the great distributors of heat over the globe, my 
chief aim has been to show the bearing which these points 
have on the grand question of secular changes of climate during 
geological epochs, more particularly in reference to that 
mystery the cause of the glacial epoch. 

In concluding this discussion regarding oceanic circulation, 
I may therefore be allowed briefly to recapitulate those points 
connected with the subject which seem to shed most light on 
the question of changes of climate. 

The complete agreement between the systems of ocean-cur- 
rents and winds not only shows that the winds are the impelling 
cause of the currents, but it also indicates to what an extent 
the directions of the currents are determined by the winds, or, 
more properly, to what an extent their directions are deter- 
mined by the direction of the winds. 

seen in Chapter II. to what an enormous extent 




THE WIND THEORY. 217 

ihe climatio conditions of the globe are dependent on the dis^ 
tribution of heat eflFected by means of ocean-currents. It has 
been there pointed out that, if the heat conveyed from inter- 
tropical to temperate and polar regions by oceanic circulation 
were restored to the former, the equatorial regions would then 
have a temperature about 55° warmer, and the high polar 
regions a climate 83° colder than at present. It follows, 
therefore, that any cause which will greatly aflFect the currents 
or greatly change their paths and mode of distribution, will of 
necessity seriously affect the climatic condition of the globe. 
But as the existence of these currents depends on the winds, 
and their direction and form of distribution depend upon the 
direction and form of distribution of the winds, any cause which 
will greatly affect the winds will also greatly affect the currents, 
and consequently will influence the climatic condition of the 
globe. Again, as the existence of the winds depends mainly 
on the difference of temperature between equatorial and polar 
regions, any cause which will greatly affect this difference of 
temperature will likewise greatly affect the winds ; and these 
will just as surely react on the currents and climatic conditions 
of the globe. A simple increase or decrease in the difference of 
temperature between equatorial and polar regions, though it 
would certainly produce an increase or a decrease, as the case 
might be, in the strength of the winds, and consequently in 
the strength of the currents, would not, however, greatly affect 
the mode of distribution of the winds, nor, as a consequence, the 
mode of distribution of the currents. But although a simple 
change in the difference of temperature between the equator 
and the poles would not produce a different distribution of 
aerial, and consequently of ocean-currents, nevertheless a 
difference in the difference of temperature between the equator 
and the two poles would do so ; that is to say, any cause that 
should increase the difference of temperature between the 
equator and the pole on the one hemisphere, and decrease that 
difference on the other, would effect a change in the dis- 
tribution of the aerial currents, which change would in turn 



2t8 CLIMATE AND TIME. 

produce a oorresponding change in the diatribution of ocean- 
currents. 

It has been shown * that an increase in the eccentricity of 
the earth's orbit tends to lower the temperature of the one 
hemisphere and to raise the temperature of the other. It 
is true that an increase of eccentricity does not afford more 
heat to the one hemisphere than to the other ; nevertheless it 
brings about a condition of things which tends to lower the 
temperature of the one hemisphere and to raise the tempera- 
ture of the other. Let us imagine the eccentricity to be at its 
superior limit, 0*07775, and the winter solstice in the aphelion. 
The midwinter temperature, owing to the increased distance of 
the sun, would be lowered enormously ; and the effect of this 
would be to cause all the moisture which now falls as rain during 
winter in temperate regions to fall as snow. Nor is this all , 
the winters would not merely be colder than now, but they 
would also be much longer. At present the summer half year 
exceeds the winter half year by nearly eight days ; but at the 
period in question the winters would be longer than the sum- 
mers by upwards of thirty-six days. The heat of the sun 
during the short summer, for reasons which have already been 
explained, would not be sufficient to melt the snow of winter ; 
80 that gradually, year by year, the snow would continue to 
accumidate on the ground. 

On the southern hemisphere the opposite condition of things 
would obtain. Owing to the nearness of the sim during the 
winter of that hemisphere, the moisture of the air woidd be pre- 
cipitated as rain in regions where at present it falls as snow. 
This and the shortness of the winter would tend to produce 
a decrease in the quantity of snow. The difference of tem- 
perature between the equatorial and the temperate and polar 
regions would therefore be greater on the northern than on 
the southern hemisphere ; and, as a consequence, the aerial 
currents of the former hemisphere would be stronger than 
those of the latter. This would be more especially the case 

• 8ee Chapter IV. 



THE WIND THEORY. 229 

with the trade-winds. The N.E. trades being stronger than 
the S.E. trades would blow across the equator, and the median 
line between them would therefore be at some distance to the 
south of the equator. Thus the equatorial waters would be 
impelled more to the southern than to the northern hemi- 
sphere ; and the warm water carried over in this manner to 
the aoathem hemisphere would tend to increase the difference 
of temperature between the two hemispheres. This change, 
again, would in turn tend to strengthen the N.E. and to weaken 
the S.E. trades, and would thus induce a still greater flow of 
equatorial waters into the southern hemisphere — a residt which 
would still more increase the difference of temperature between 
the northern and southern hemisphere, and so on — the one 
cause 80 reacting on the other as to increase its effects, as was 
shown at length in Chapter IV. 

It was this mutual reaction of those physical agents which 
led, as was pointed out in Chapter IV., to that extraordinary 
condition of climate which prevailed during the glacial 
epoch. 

There is another circumstance to be considered which per- 
haps more than any thing else would tend to lower the tem- 
perature of the one hemisphere and to raise the temperature of 
the other ; and this is the diaplacement of the great equaiorial 
current During a glacial period in the northern hemisphere 
the median line between the trades would be shifted very con- 
siderably south of the equator ; and the same would necessarily 
be the case with the great equatorial currents, the only 
difference being that the equatorial currents, other things 
being equal, would be deflected farther south than the median 
line. For the water impelled by the strong N.E. trades would 
be moving with greater velocity than the waters impelled by 
the weaker S.E. trades, and, of course, would cross the median 
line of the trades before its progress southwards coidd be 
arrested by the counteracting influence of the S.E. trades. Let 
us glance briefly at the results which would follow from such a 
condition of things. In the first place, as was shown on former 



ffo CLIMATE AND TIME. 

oeoMions/ were the equatorial carreat of tlie Atlaxitie (the 
feeder of the Gulf-«tream) shifted oonsiderablT mmth of its 
prebeut positioji, it would not bifurcate, as it now does, off 
Cape tit, lioque, owing to the fact tliat the whole of the wmten 
would strike obliquely againi^t the Brazilian coast and thus 
be deflected into the Southern Ocean* The effect prodnced on 
the cliiuate of the North Atlantic and North- Western Europe 
by the withdrawal of the water forming the Gulf-stream, may 
be conceived from what has already been stated concerning the 
amount of heat <xinveyed by that stream* The heat thua with- 
drawn from the North Atlantic would go to raise the tempera- 
ture of the Southern Ocean and antarctic regions. A similar 
result would take place in the Pacific Ocean. Were the equa- 
torial current of that ocean removed greatly to the south of its 
prcHimt {x>Hition, it would not then impinge and be deflected 
upon the AHiutic cotiHt, but upon the continent of Australia ; 
and the greater jK^rtion of it.s waters would then pass south- 
ward into the Soutlicrn Ocean, while that portion passing 
round the nortli of Auntralia (owing to the great strength of the 
N.E. tradcH) would rather How into the Indian Ocean than 
turn round, aH now, along the east coast of Asia by the Japan 
Islandii. The stoppage of the Japan current, combined with 
the diNplacement of the equatorial current to the south of the 
ecjuator, would greatly lower the temperature of the whole of 
the North l*aoitio and adjoining continents, and raise to a cor- 
iHMpcmding degree the temperature of the South Pacific and 
Soutliorn Ociuin. Again, the waters of the ecjuatorial current 
of the Indian Oooun (owing to the opposing N.E. trades), 
would not, art at pri'sont, find their way round the Cape of 
U(HhI lli>iK» inti> the North Atlantic, but would be deflected 
south wuihIs into the Antarctic 8t\i. 

Wu havo in the pivscnt state of things a striking example of 
the extent to which the uuHliau lino between the two trades 
inuy )k> shit^inl. ami the }HKsitiouof the great eiiuatorial currents 
uf the 0iH>uu may Ik^ ulUTtiHl, by a slight difference in the 

« Pkil llttg. fv^r August. IS6«. bVVnmn'. 1867, March, 1870 ; 8«e Chap. lY 



THE WIND THEORY. sji 

relatiYe strength of the two aerial currents. The S.E. trades 
are at present a little stronger than the N.E. ; and the con- 
aequence is that they blow across the equatoa into the northern 
hemisphere to a distance sometimes of 10 or 15^, so that the 
mean position of the median line lies at least 6 or 7 degrees 
north of the equator. 

And it is doubtless owing to the superior strength of the 
S.E. trades that so much warm water crosses the equator from 
the South to the North Atlantic, and that the main portion of 
the equatorial current flows into the Caribbean Sea rather than 
along the Brazilian coast. Were the two trades of equal 
strength, the transferrence of heat into the North Atlantic from 
the southern hemisphere by means of the Southern Atlantic 
and equatorial currents would be much less than at present. 
The same would also hold true in regard to the Pacific. 

Ocean-currents in Relation to the Distribution of Plants and 
Animals, — In the fifth and last editions of the "Origin of 
Species," Mr. Darwin has done me the honour to express his 
belief that the foregoing view regarding alternate cold and 
warm periods in north and south during the glacial epoch 
explains a great many facts in connection with the distribution 
of plants and animals which have always been regarded as 
exceedingly puzzling. 

There are certain species of plants which occur alike in the 
temperate regions of the southern and northern hemispheres. 
At the equator these same temperate forms are foimd on 
elevated mountains, but not on the lowlands. How, then, did 
these temperate forms manage to cross the equator from the 
northern temperate regions to the southern, and vice versd f 
Mr. Darwin's solution of the problem is (in his own words) as 
follows ; — 

" As the cold became more and more intense, we know that 
arctic forms invaded the temperate regions ; and from the facts 
just given, there can hardly be a doubt that some of the more 
vigorous, dominant, and widest-spreading temperate forms in- 
vaded the equatorial lowlands. The inhabitants of these hot 



ass CLIMATE AND TIME. 

lowlands would at the same time have migrated to the tropical 
and subtropical regions of the south ; for the southern hemi* 
sphere was at this period warmer. On the decline of the 
glacial period, as both hemispheres gradually recovered their 
former temperatures, the northern temperate forms living on 
the lowlands under the equator would have been driven to their 
former homes or have been destroyed, being replaced by the 
equatorial forms returning from the south. Some, however, 
of the northern temperate forms would almost certainly have 
ascended any adjoining high land, where, if sufficiently lofty, 
they would have long survived like the arctic forms on the 
mountains of Europe." 

" In the regular course of events the southern hemisphere 
would in its turn be subjected to a severe glacial period, with 
the northern hemisphere rendered warmer; and then the 
southern temperate forms would invade the equatorial low- 
lands. The northern forms which had before been left on the 
mountains would now descend and mingle with the southern 
forms. These latter, when the warmth returned, would return 
to their former homes, leaving some few species on the moim- 
tains, and carrying southward with them some of the northern 
temperate forms which had descended from their moimtain 
fastnesses. Thus we should have some few species identically 
the same in the northern and southern temperate zones and on 
the mountains of the intermediate tropical regions *' (p. 339, 
sixth edition). 

Additional light is cast on this subject by the results 
already stated in regard to the enormous extent to which the 
temperature of the equator is affected by ocean-currents. Were 
there no transferrence of heat from equatorial to temperate 
and polar regions, the temperature of the equator, as has 
been remarked, would probably be about 56° warmer than at 
present. In such a case no plant existing on the face of the 
globe could live at the equator unless on some elevated moun- 
tain region. On the other hand, were the quantity of warm 
water which is being transferred from the equator to l)e very 



THE WIND THEORY. tjj 

maoli increased, the temperature of inter- tropical latitudes 
might be so lowered as easily to admit of temperate species of 
plants growing at the equator. A lowering of the tempera- 
ture at the equator some 20^ or 30^ is all that would be 
required ; and only a moderate increase in the volume of the 
currents proceeding* from the equator, taken in connection with 
the effects flowing from the following considerations, might 
suffice to produce that result. During the glacial epoch, when 
the one hemisphere was under ice and the other enjoying a 
warm and equable climate, the median line between the trades 
may haye been shifted to almost the tropical line of the warm 
hemisphere. Under such a condition of things the warmest 
part would probably be somewhere about the tropic of the 
warm hemisphere, and not, as now, at the equator ; for since 
all, or nearly all, the surface-water of the equator woidd then 
be impelled over to the warm hemisphere, the tropical regions 
of that hemisphere would be receiving nearly double their 
present amount of warm water. 

Again, as the equatorial current at this time would be 
shifted towards the tropic of the warm hemisphere, the surface- 
water would not, as at present, be flowing in equatorial regions 
parallel to the equator, but obliquely across it from the cold to 
the warm hemisphere. This of itself would tend greatly to 
lower the temperature of the equator. 

It follows, therefore, as a necessary consequence, that during 
the glacial epoch, when the one hemisphere was under snow 
and ice and the other enjoying a warm and equable climate, 
the temperature of the equator would be lower than at present. 
But when the glaciated hemisphere (which we may assume to 
be the northern) began to grow warmer and the climate of the 
southern or warm hemisphere to get colder, the median line of 
the trades and the equatorial currents of the ocean also would 
begin to move back from the southern tropic towards the 
equator. This would cause the temperature of the equator to 
rise and to continue rising until the equatorial currents reached 
their normal position. When the snow began to accumulate 



J34 CLIMATE AND TIME. 

on the southern hemisphere and to disappear on the northern, 
the median line of the trades and the equatorial currents of 
the ocean would then begin to move towards the northern 
tropic as they had formerly towards the southern. The tem- 
perature of the equator woidd then again begin to sink, and 
continue to do so imtil the glaciation of the southern hemi- 
sphere reached its maximum. This oscillation of the thermal 
equator to and fro across the geographical equator would 
continue so long as the alternate glaciation of the two hemi- 
spheres continued. 

This lowering of the temperature of the equator during the 
severest part of the glacial epoch will help to explain the 
former existence of glaciers in inter-tropical regions at no yery 
great elevation above the sea-level, evidence of which appears 
recently to have been found by Professor Agassiz, Mr. Belt, and 
others. 

The glacial epoch may be considered as contemporaneous in 
both hemispheres. But the epoch consisted of a succession of 
cold and warm periods, the cold periods of one hemisphere coin- 
ciding with the warm periods of the other, and vice tersd. 

Migration across the Equator. — Mr. Belt* and others have 
felt some difficidty in understanding how, according to theory, 
the plants and animals of temperate regions could manage to 
migrate from one hemisphere to the other, seeing that in their 
passage they would have to cross the thermal equator. The 
oscillation to and fro of the thermal equator across the 
geographical, removes every difficulty in regard to how the 
migration takes place. When, for example, a cold period on 
the northern hemisphere and the corresponding warm one on 
the southern were at their maximum, the thermal equator 
would by this time have probably passed beyond the Tropic of 
Capricorn. The geographical equator would then be enjoying 
a subtropical, if not a temperate condition of climate, and the 
plants and animals of the northern hemisphere would manage 
then to reach the equator. When the cold began to abate 

* Quarterly Journal of Science for October, 1874. 



THE WIND THEORY. 



«35 



on the northern and to increase on the southern hemi8phei*e, 
the thermal equator would commence its retreat towards the 
geographical. The plants and animals from the north, in order 
to escape the increasing heat as the thermal equator approached 
them, would begin to ascend the mountain heights ; and when 
that equator had passed to its northern limit, and the geographical 
equator was again enjoying a subtropical condition of climate, 
the plants and animals would begin to descend and pursue 
their journey southwards as the cold abated on the southern 
hemisphere. 



IT 



CHAPTER XV. 

WARM INTEK-GLACIAL PERIODS. 

AUflmata Cold and Warm Periods. — Warm Inter-glacial Periods a Test ol 
Theoriet. — Beaaon why their Occurrence haa not been hitherto zecogniaed* 
— Instances of Warm Inter-glacial Periods. — Dranse, Diimten, Uozne, 
Chapelhiill, Craiglockhart, Leith-Walk, Kedhall Quarry, Beith, Grofthead, 
Kilmaurs, Sweden, Ohio, Cromer, Mundeslc^y, &c, &c. — Cave and River 
Depotfits. — Occurrence of Arctic and Warm Animals in some Beds accounted 
lor. — Mr. Boyd Dawkins's Objections. — Occurrence of Southern Shells in 
Glacial Deposits. — Evidence of Warm Inter-glacial Periods from Mineral 
Borings. — Strialed Pavements. — he.is<^n why Inier-g acial Land -surfaces 
uru so rare. 

Alternate Cold and Warm Periods, — If the theory developed 
in the foregoing chapters in reference to the cause of secular 
changes of climate he correct, it follows that that long age 
known as the glacial epoch did not, as has hitherto been 
generally supposed, consist of one long unbroken period of 
cold and ice. Neither did it consist, as some have con- 
cluded, of two long periods of ice with an intervening mild 
period, but it must have consisted of a long succession of cold 
and warm periods; the warm periods of the one hemisphere 
corresponding in time with the cold periods of the other and 
vice versa. It follows also from theory that as the cold periods 
became more and more severe, the warm intervening periods 
would become more and more warm and equable. As the ice 
began to accumulate during the cold periods in subarctic and 
temperate regions in places where it previously did not exist, 
so in like manner during the corresponding warm periods it 
would begin to disappear in arctic regions where it had held 
enduring sway throu<jfhout the now closing cycle. As the cold 

riods in the southern hemisphere became more and more 



INTER-GLACIAL PERIODS. 237 

severe, the ice would continue to advance northwards in the 
temperate regions; but at that very same time the inter- 
vening warm periods in the northern hemisphere would 
become warmer and warmer and more equable, and the ice 
of the arctic regions would continue to disappear farther 
and farther to the north, till by the time that the ice had 
reached a maximum during the cold antarctic periods, Green- 
land and the arctic regions would, during the warm interven- 
ing periods, be probably free of ice and enjoying a mild and 
equable climate. Or we may say that as the one hemisphere 
became cold the other became warm, and when the cold 
reached a maximum in the one hemisphere, the warmth would 
reach a maximum in the other. The time when the ice had 
reached its greatest extension on the one hemisphere would be 
the time when it had disappeared from the other. 

Inter-glacial Periods a Test of Theones. — Here we have 
the grand crucial test of the truth of the foregoing theory 
of the cause of the glacial epoch. That the glacial epoch 
should have consisted of a succession of cold and warm 
periods is utterly inconsistent with all previous theories which 
have been advanced to account for it. What, then, is the 
evidence of geology on this subject? If the glacial epoch 
can be proved from geological evidence to have consisted of 
such a succession of cold and warm periods, then I have little 
doubt but the theory will soon be generally accepted. But 
at the very outset an objection meets us, viz., why call an 
epoch, which consisted as much of warm periods as of cold, a 
glacial epoch, or an " Ice Age," as Mr. James Geikie tersely 
expresses it ? Why not as well call it a warm epoch as a cold 
one, seeing that, according to theory, it was just as much a 
warm as a cold epoch ? The answer to this objection will be 
fully discussed in the chapter on the Reason of the Imperfection 
of Geological Records. But in the meantime, I may remark 
that it will be shown that the epoch known as the glacial has 
been justly called the glacial epoch or " Ice Age," because the 
geological evidences of the cold periods remain in a remarkably 



ijS CLIMATE AND TIME. 

perfect state, whilst the evidences of the warm periods have to 
a great extent disappeared. The reason of this difference in 
the two cases will be discussed in the chapter to which I have 
referred. Besides^ the condition of things during the cold 
periods was so extraordinary, so exceptional, so totally different 
from those now prevailing, that even supposing the geological 
records of the warm periods had been as well preserved as 
those of the cold, nevertheless we should have termed the 
epoch in question a glacial epoch. There is yet another reason, 
however, for our limited knowledge of warm inter-glacial 
periods. Till very lately, little or no attention was paid by 
geologists to this part of the subject in the way of keeping 
I'ecords of cases of inter-glacial deposits which, irom time to 
time, have been observed. Few geologists ever dreamt of 
such a thing as warm periods during the age of ice, so that 
when intercalated beds of sand and gravel, beds of peat, roots, 
branches, trunks, leaves, and fruits of trees were found in the 
boulder clay, no physical importance was attached to them, 
and consequently no description or record of them ever kept. 
In fact, all such examples were regarded as purely accidental 
and exceptional, and were considered not worthy of any special 
attention. A case which came imder my own observation will 
illustrate my meaning. An intelligent geologist, some years 
ago, read a paper before one of our local geological societies, 
giving an account of a fossiliferous bed of clay found inter- 
calated between two distinct beds of till. In this intercalated bed 
were found rootlets and stems of trees, nuts, and other remains, 
showing that it had evidently been an old inter-glacial land 
surface. In the transactions of the society a description of the 
two beds of till was given, but no mention whatever was made 
of the intercalated bed containing the organic remains, although 
this was the only point of any real importance. 

Since the theory that the glacial epoch resulted from a high 
state of eccentricity of the earth's orbit began to receive some 
little acceptance, geologists have paid a good deal of attention 
of intercalated beds in the till containing organic 




INTER-GLACIAL PERIODS. 239 

remains, and the result is that we have already a great body of 
evidence of a geological nature in favour of warm inter-glacial 
periods, and I have little doubt that in the course of a few 
years the former occurrence of warm inter-glacial periods will 
be universally admitted. 

I shall now proceed to give a very brief outline of the 
eWdence bearing on the subject. But the cases to which I 
shall have to refer are much too numerous to allow mo to 
enter into details. 

Inter-glacial BcdH of B'cifzerland, — The first geologist, so far 
as I am aware, who directed attention to evidence of a break in 
the cold of the glacial epoch was M. Morlot. It is now twenty 
years ago since he announced the existence of a warm period 
during the glacial epoch from geological evidence connected 
with the glacial drift of the Alps.* 

The rivers of Switzerland, he found, show on their banks 
three well-marked terraces of regularly stratified and well- 
rounded shingle, identical with the modem deposits of the 
rivers. They stand at 50, 100, and 150 feet above the present 
level of the rivers. These terraces were evidently formed by 
the present sj'stem of rivers when these flowed at a higher 
level, and extend up the Alps to a height of from 3,000 to 
4,000 feet above the level of the sea. There is a terrace 
bordering the Bhine at Gamischollas, above Disentis, 4,400 
feet above the level of the sea, proving that during the period 
of its formation the Alps were free of ice up to the height of 
4,400 feet above the sea-level. It is well known that a glacial 
period must have succeeded the formation of these drifts, for 
they are in many places covered with erratics. At Geneva, for 
example, an erratic drift nearly 50 feet thick is seen to rest on 
the drift of the middle terrace, which rises 100 feet above the 
level of the lake. But it is also evident that a glacial period 
must have preceded the formation of the drift beds, for they 
are found to lie in many places upon the imstratified boulder 

• See a paper by M. iforlot, on ** The Post-Tertiary and Quaternary Formft* 
tions of Switzerland." Edin. Now PhiL Journal, Mew Series, vol. ii, 1S56. 




t40 CLIMATE AXD TIME. 

ehxj or till, H. Morlot observed in the neighboarhood of 
Clareuis, from 7 to 9 feet of drift resting upon a bed of true 
till 40 (tei thick ; the latter was composed of a compact blue 
clay, containing worn and scratched alpine boolders and with- 
out any tmcc of stratification. In the gorge of Dranse, near 
Thoron, M. Morlot found the whole three formations in a 
direct superimposed series. At the bottom was a mass of 
compact till or boulder clay, 12 feet thick, containing boulders 
of alpine limestone. Over this mass came regularly stratified 
beds loO feet thick, made up of rounded pebbles in horizontal 
bccls. Above this again lay a second formation of imstratified 
boulder clay, with erratic blocks and striated pebbles, which 
constituUxl tlie left lateral moraine of the great glacier of the 
lihone, when it advanced for the second time to the Lake of 
Oenevii. A condition of things somewhat similar was observed 
by M. iHchcr in the neighbourhood of Berne. 

ThcHO factH, M. Morlot justly considers, prove the existence 
of two glacial periods separated by an intermediate one, during 
which the ice, which had not only covered Switzerland, but 
the greater part of Europe, disappeared even in the principal 
valleys of the Alps to a height of more than 4,400 feet above 
the present level of the sea. This warm period, after continu- 
ing for long ages, was succeeded by a second glacial period, 
during which the country was again covered with ice as before. 
M. Morlot even suggests the possibility of these alternations of 
cold and warm periods depending upon a cosmical cause. 
" Wild as it may have appeared," he says, ** when first started, 
the idea of general and periodical eras of refrigeration for our 
planet, connected perhaps with some cosmic agency, may even- 
tually prove correct."* 

Shortly afterwards, evidence of a far more remarkable 
character was found in the glacial drift of Switzerland, 
namely, the famous lignite beds of Diimten. In the vicinity 
of XTtinach and Diimten, on the Lake of Zurich, and near 
Mdrachwyli on the Lake of Constance, there are beds of coal or 

* Ediiu New Phil. Joam., New Scries, toL u.» p. 2S. 



INTER-GLACIAL PERIODS, 341 

lignite, nearly 12 feet thick, lying directly on the boulder clay. 
Overlying these beds is another mass of drift and clay 30 
feet in thickness, with rounded blocks, and on the top of this 
upper drift lie long angular erratics, which evidently have 
been transported on the back of glaciers.* Professor Vogt 
attributes their transport to floating ice ; but he evidently 
does so to avoid the hypothesis of a warm period during the 
glacial epoch. 

Here we have proof not merely of the disappearance of the 
ice during the glacial epoch, but of its absence during a period 
of sufficient length to allow of the growth of 10 or 12 feet 
of coal. Professor Heer thinks that this coal-bed, when in 
the condition of peat, must have been 60 feet thick ; and as- 
suming that one foot of peat would be formed in a century, he 
concludes that 6,000 years must have been required for the 
growth of the coal plants. According to Liebig, 9,600 years 
would be required. This, as we have already seen, is about the 
average duration of a warm period. 

In these beds have been found the bones of the elephant 
{E, Merkit), stag, cave-bear, and other animals. Numerous 
insects have also been met with, which further prove the warm, 
mild condition of climate which must have prevailed at the 
time of the formation of the lignite. 

At Hoxne, near Diss, in Suffolk, a black peaty mass several 
feet thick, containing fragments of wood of the oak, yew, and 
fir, was found overlying the boulder olay.t Professor Vogt be- 
lieves that this peat bed is of the same age as the lignite beds 
of Switzerland. 

In the glacial drift of North America, particularly about 
Lake Champlain and the valley of the St. Lawrence, there is 
similar evidence of two glacial periods with an intervening non- 
glacial or warm period. + 

• Vogfe ** Lectures on Mnn," pp. 318 — 321. 

t Beu Mr. Prestwich on Flint Implements, Phil. Trans, for 1860 and 1S64. 
Lyell'e ** Antiquity of Man," Second Edition, p. 168. 

X Edin. New Phil, .lourn., New Series, vol. ii., p. 28. Silliman'g Jymn^ 
rol. xlvii., p. 269 (1844). 



HS CLIMATE AND TIME. 

Glacial and Inter-glacial Periods of the Southern Hemisphert 
{South Africa). — Mr. G. W. Stow, in a paper ou the " GFeology 
of South Africa," * describes a recent glaciation extending over 
a large portion of Natal, British Kaffraria, the Kaga and Krome 
mountains, which he attributes to the action of land-ice. He 
sums up the phenomena as follows : — " The rounding off of the 
hills in the interiors of the ancient basins ; the numerous dome- 
shaped {roches moutonnee) rocks ; the enormous erratic boulders 
in positions where water could not have carried them ; the 
frequency of unstratified clays — clays with imbedded angular 
boulders ; drift and lofty mounds of boulders ; large tracts of 
country thickly spread over with unstratified clays and super- 
imposed fragments of rock ; the 01iphant*s-Hock clay, and the 
vast piles of Enon conglomerate." In addition to these results 
of ice-action, he records the discovery by himself of distinct 
ice-scratches or groovings on the surface of the rocks at Eeit- 
Poort in the Tarka, and subsequently t the discovery by Mr, 
G. Gilfillan of a large boulder at Pniel with atrice distinctly 
marked upon it, and also that the same observer found that 
almost every boulder in the gravel at " Moonlight Rush " had 
unmistakable strise on one or more sides. 

In South Africa there is evidence not only of a glacial con- 
dition during the Pliocene period, but also of a warmer climate 
than now prevails in that region. " The evidence," says Mr. 
Stow, " of the Pliocene shells of the superficial limestone of the 
Zwartkops heights, and elsewhere, leads us to believe that the 
climate of South Africa must have been of a far more tropical 
character than at present. 

*' Take, for instance, the characteristic Venericardia of that 
limestone. This has migrated along the coast some 29° or 
30^ and is now found within a few degrees of the equator, 
near Zanzibar, gradually driven, as I presume it must have 
been, further and fiirther north by a gradual lowering of the 
temperature of the more southern parts of this coast since the 
limestone was deposited*" 

* Qoart. Joum. Qeol. Soc., vol. xxvii., p. >53^. f Ibid., vol. xxviii., p. 17 



INTER-GLACIAL PERIODS. 243 

''DuiiDg the formation of the shell-banks in the Zwartkops 
eatuary, younger than the Pliocene limestone, the immense 
number of certain species of shells, which have as yet been 
found living only in latitiides nearer the equator, point to a 
somewhat similar though a more modified change of tem- 
perature." 

Inter-glacial Beds of ScotUtnd. — Upwards of a dozen years ago, 
Professor Geikie arrived, from his own observations of the 
glacial drift of Scotland, at a similar conclusion to that of M. 
Morlot regarding the intercalation of warm periods during the 
glacial epoch ; and tlie facts on which Professor Geikie'e con- 
clusions were based are briefly as follows. In a cliff of boulder 
clay on the banks of the Slitrig Water, near the town of 
Hawick, he observed a bed of stones or shingle. Over the 
lower stratum of stones lay a few inches of well-stratified sand, 
silt, and clay, some of the layers being black and peaty, 
with enclosed tegefnhle fibres in a crumbling state.* There were 
some 30 or 40 feet of boulder clay above these stratified beds, 
and 15 or 20 feet under them. The stones in the shingle 
band were identical with those of the boulder clay, but they 
showed no striations, and were more rounded and water-worn, 
and resembled in every respect the stones now lying in the bed 
of the Slitrig. The section of the cliff stood as \mder : — 



1. Vegfitablo soil. 

2. Bdulder clay, thirty to forty feet 

3. yellowish gravelly sand. 

stratified bedH I \- P°«ty •*!' '^d ^-l"?- . 

0. i^ me ferru^nous sand. 

6. Course shinprle, two to three feet. 

7. Coarse, btifi' boulder clay, fifteen to twenty feet. 



A few more cases of intercalation of stratified materials in 
the true till were also found in the same valley. 

In a cliff of stiff brown boulder clay, about 20 feet high, 
on the banks of the Carmichael Water, Lanarkshire, Professor 

• <' Glacial Drift of Scotland," p. 54. 



144 CUM ATE AND TIME. 



GteQde obflenred a ttntified bed of olaj about 8 or 4 inches 
in ihickneM. About a mile bigber up tbe stream^ be fennd a 
Miries of beds of gravely sand, and clay in tbe true HU. '' A 
tbin seam oi peaty matter!^ be saysy '^was obeenred to run for a 
few incbes along tbe bottom of a bed of clay and tben 
disappeary wbile in a band of fine laminated day witb tbin 
sandy partings occasional fragmenU of mouldering tcood were 
found/'* 

At Cbapelball, near Airdrie, a sand-bed bas been eztensiTely 
mined under about 114 feet of tilL Tbis bed of finely stratified 
sand is about 20 feet tbiok. In it were found lenticular beds 
of fine pale-coloured day containing layers of peat and decaying 
twigs and brancbes. Professor Geikie found tbe vegetable 
fibres, thougb mucb decayed, still distinct, and tbe substance 
wben put into tbe fire burned with a dull lambent flame. Un» 
derlying these stratified beds, and forming the floor of the 
mine, is a deposit of t/te (rue till about 24 feet in thickness. In 
another pit adjoining, the till forming the floor is 30 feet thick, 
but it is sometimes absent altogether, so as to leave the sand- 
beds resting directly on the sandstone and shale of the coal- 
measures. At some distance from this sand-pit an old buried 
river cbannd was met with in one of the pit workings. This 
channel was found to contain a coating of boulder clay, on which 
the laminated sands and clays reposed, showing, as Professor 
Oeikie has pointed out, that this old chaiiDcl had been filled 
with boulder clay, and then re-excavated to allow of the depo- 
sition of the stratified deposits. Over all lay a thick mantle of 
boulder clay which buried the whole. 

A case somewhat similar was found by Professor Nicol in 
a cutting on the Edinburgh and Leith Railway. In many 
places the till bad been worn into hollows as if part of it had 
been removed by the action of running water. f One of these 
boUowSy about 5 or 6 feet wide by 3 or 4 feet deep, closely 
resembled tbe channel of a small stream. It was also filli^l 

• "Gkoial Diift of Scotland," p. 58. 
t Qiiut. JouTD. GuoL 8oo., toI. ▼., p. 23. 



INTER-GLACIAL PERIODS. 2+5 

with gravel and sand, in all respects like that found in such a 
stream at the present day. It was seen to exhibit the same 
characters on both sides of the cutting, but Professor Nicol was 
unable to determine how far it may have extended beyond; 
but he had no doubt whatever that it had been formed by a 
stream of water. Over this old water-course was a thick de- 
posit of true till. 

In reference to the foregoing cases, Professor Geikie makes 
the following pertinent remarks : — " Here it is evident that 
the scooping out of this channel belongs to the era of the 
boulder clay. It must have been effected during a pause in 
the deposition of the clay, when a run of water could find its 
way along the inequalities of the surface of the clay. This 
pause must have been of sufficient duration to enable the 
runnel to excavate a capacious channel for itself, and leave in 
it a quantity of sand and shingle. We can scarcely doubt 
that when this process was going on the ground must have 
been a land surface, and could not have been under the sea. 
And lastly, we see from the upper boulder chiy that the old 
conditions returned, the water-course was choked up, and 
another mass of chaotic boulder clay was tumbled down upon 
the face of the country. This indicates that the boulder clay 
is not the result of one great catastrophe, but of slow and 
silent, yet mighty, forces acting sometimes with long pauses 
throughout a vast cycle of time." • 

At Craiglockhart Hill, about a mile south of Edinburgh, 
an extensive bed of fine sand of from one to three feet in 
thickness was found between two distinct masses of true boulder 
clay or till. The sand was extensively used for building 
purposes during the erection of the city poorhouse a few years 
ago. In this sand-bed I found a great many tree roots in the 
position in which they had grown. During the time of the 
excavations I visited the place almost daily, and had every 
opportunity of satisfying myself that this sand-bed, prior to 
the time of the formation of the upper boulder clay, must have 

• «* Gkcial Dria of Scotland,'* p. 64. 



#46 CLIMATE AND TIME. 

been a land surface on which the roots had grown. In no oaae 
did I find them penetrating into the upper boulder clay, and in 
several places I found stones of the upper clay resting directly 
on the broken ends of the roots. These roots were examined 
by Professor Balfour, but they were so decayed that he was 
unable to determine their character. 

In digging a foundation for a building in Leith Walk, Edin- 
burgh, a few years ago, two distinct beds of sand were passed 
through, the upper, about 10 feet in thickness, rested upon what 
appeared to be a denuded surface of the lower l)ed. In this 
lower bed, which evidently had been a land surface, numbers 
of tree roots were found. I had the pleasure of examining 
them along with my friend Mr. C. W. Peach, who first directed 
my attention to them. In no instance were the roots found in 
the upper bed. That these roots did not belong to trees which 
had grown on the present surface and penetrated to that depth, 
was further evident from the fact that in one or two cases we 
found the roots broken off at the place where they had been 
joined to the trunk, and there the upper sand-bed over them 
was more than 10 feet in thickness. If we assume that the 
roots belonged to trees which had grown on the present surface, 
then we must also assume, what no one would bo willing to 
admit, that the trunks of the trees had grown downwards into 
the earth to a depth of upwards of ten feet. I have shown 
these roots to several botanists, but none of them could deter- 
mine to what trees they belonged. The surface of the ground 
at the spot in question is 45 feet above sea-level. Mr. Peach 
and I have found similar roots in the under sand-bed at 
several other places in the same neighbourhood. That they 
belong to an inter -glacial period appears probable for the follow- 
ing reasons : — (1.) This upper sand-bed is overlaid by a tough 
clay, which in all respects appears to be the same as the Porto- 
bello clay, which we know belongs to the glacial series. In 
company with Mr. Bennie, I found the clay in some places to 
be contorted in a similar manner to the Portobello clays. (2.) 
id-pit about one or two hundred yards to the west of 




INTER-GLACIAL PERIODS. 147 

where the roots were found, the sand-bed was found contorted 
in the most extraordinary manner to a depth of about 15 feet. 
In fact, for a space of more than 30 feet, the bedding had been 
completely turned up on end without the fine layers being in 
the least degree broken or disarranged, showing that they had 
been upturned by some enormous powers acting on a largo mass 
of the sand. 

One of the best examples of true till to be met with in the 
neighbourhood of Edinburgh is at Redhall Quarry, about throe 
miles to the south-west of the city. In recently opening up a 
new quarry near the old one a bed of peat was found inter- 
calated in the thick mass of till overlying the rock. The clay 
overlying and underlying the peat-bed was carefully examined 
by Mr. John Henderson,* and found to be true till. 

In a quarry at Overtown, near Beith, Ayrshire, a sedimentary 
bed of clay, intercalated between two boulder clays, was some 
years ago observed by Mr. Robert Craig, of the Glasgow 
Geological Society. This bed filled an elliptical basin about 130 
yards long, and about 30 yards broad. Its thickness averaged 
from one to two feet. This sedimentary bed rested on the till 
on the north-east end of the basin, and was itself overlaid on 
the south-west end by the upper bed of till. The clay bed was 
found to be full of roots and stems of the common hazel. That 
these roots had grown in the position in which they were found 
was evident from the fact that they were in many places fo\md 
to pass into the " cutters *' or fissures of the limestone, and were 
here found in a flattened form, having in growing accommodated 
themselves to the size and shape of the fissures. Nuts of the 
hazel were plentifully found.t 

At Hillhead, some distance from Overtown, there is a similar 
intercalated bed full of hazel remains, and a species of fresh- 
water Ontracoda was detected by Mr. David Robertson. 

In a railway cutting a short distance from Beith, Mr. Craig 
pointed out to my colleague, Mr. Jack, and myself, a thin 

• Ttjiub. Edin. Geol. 80c., vol. ii., p. 391. 

f Trans, of Geol. Soc. of Glaagow, vol. It., p. I4d. 

12 



h8 climate and time. 

layer of peaty matter, extending for a considerable distance 
between an upper and lower mass of till ; and at one place we 
found a piece of oak about four feet in length and about seven 
or eight inches in thickness. This oak boulder was well 
polished and striated. 

Not far from this place is the famous Crofbhead inter-glacial 
bedy so well known from the description given by Mr. James 
G^kie and others that I need not here describe it. I had the 
pleasure of visiting the section twice while it was well exposed, 
once, in company with Mr. James Geikie, and I do not 
entertain the shadow of a doubt as to its true inter-glaciol 
character. 

In the silt, evidently the mud of an inter-glacial lake, were 
found the upper portion of the skull of the great extinct ox 
(Baa primi(/en Ills) y horns of the Irish elk or deer, and bones of 
the horse. In the detailed list of the lesser organic remains 
found in the intercalated peat-bed by Mr. J. A. Mahony,* are 
the following, viz., three species of Desmidacea*, thirty-one 
species of DiaiomaccfB, eleven species of mosses, niue species of 
phanerogamous plants, and several species of annelids, Crustacea, 
and insects. This list clearly shows that the inter-glacial period, 
represented by these remains, was not only mild and warm, but 
of considerable duration. Mr. David Kobertson found in the 
clay under the peat several species of Osfracoda. 

The well-known Kilmaurs bed of peaty mutter in which the 
remains of the mammoth and reindeer were found, has now by 
the researches of the Geological Survey been proved to be of 
inter-glacial age.f 

In Ireland, as shown by Professors Hull and Harkness, the 
inter-glacial beds, called by them the ** manure gravels," con- 
tain numerous fragments of shells indicating a more genial 
climate thjm prevailed when the boulder clays lying above and 
below them were formed. J 

• Gcol. Mag., vi., p. 391. 

t be© " Memoirs of Geologi<al Survey oi Scotland," Explanation of sheet 22, 
p. 29. 8ee also Tr:»nH. Glasgow Geol. ^Soc., iv., p. 150. 
X "toat Ice Age," p. 374. 




INTER-GLACIAL PERIODS. 249 

In Sweden inter-glacial beds of fresh-water origin, contain- 
ing plants, have been met with by Herr Nathorst and also by 
Herr Holmstrom.* 

In North America Mr. Whittlesey describes inter-glacial 
beds of blue clay enclosing pieces of wood, intercalated with 
beds of hard pan (till). Professor Newberry found at German- 
town, Ohio, an immense bed of peat, from 12 to 20 feet in 
thickness, underlpng, in some places 30 feet, and in other 
places as much as 80 feet, of till, and overlying drift beds. The 
uppermost layers of the peat contain undecomposed sphagnous 
mosses, grasses, and sedges, but in the other portions of the 
bed abundant fragments of coniferous wood, identified as red 
cedar {Juniper us virginiana), have been found. Ash, hickory, 
sycamore, together with grape-^ines and beech-leaves, were 
also met with, and with these the remains of the mastodon 
and great extinct beaver. t 

Intcr-glacial Beds of England, — Scotland has been so much 
denuded by the ice sheet with which it was covered during the 
period cf maximum glaciation that little can be learned in this 
part of the island regarding the early history of the glacial 
epoch. But in England, and more especially in the south- 
eastern portion of it, matters are somewhat different. We have, 
in the Norwich Crag and Chillesford beds, a formation pretty 
well developed, w hich is now generally regarded as lying at 
the base of the Glacial Series. That this formation is of a 
glacial character is evident from the fact of its containing 
shells of a northern type, such as Leda lanceolata^ Cardium 
Groenlandicum, Lucina borealis, Cyprina Islandica, Panop<sa 
Norvegicay and Mya tnincata. But the glacial character of the 
formation is more strikingly brought out, as Sir Charles Lyell 
remarks, by the predominance of such species as Rhynchonella 
psittacea, Tellina calcarea^ Astarte borealis, Scalaria Orohilandica^ 
and Fusus carinatus, 

» •' Great Ice Ago," p. 384. 

t <' Geologictd Survey of Ohio, 1869," p. 165. See alio «* Great loe An" 
chap. xxTiii. 



»So CLIMATE AND TIME. 

The ** Forest Beds.** — ^Immediately following thiB in the order 
of time comes tlie fiunous ^^ Forest Bed'' of Cromer. This 
buried forest has been traced for more than forty miles along 
the coast from Cromer to near Kessengland, and consists of 
stumps of trees standing erect, attached to their roots, peno* 
trating the original soil in which they grew. Here and in the 
overlying fluvio-marine beds we have the first evidence of at 
least a temperate, if not a warm, inter-glacial period. This is 
evident from the character of the flora and fauna belonging to 
these beds. Among the trees we have, for example, the Scotch 
and spruce fir, the yew, the oak, birch, the alder, and the com- 
mon sloe. There have also been found the white and yellow 
water-lilies, the pond-weed, and others. Amongst the mam- 
malia have been met with the Elephas nieridionalis, also found 
in the Lower Pliocene beds of the Val d'Amo, near Florence ; 
Ekphas anfiquuSf Hippopotamus major, Rhinoceros Etruseus, the 
two latter Val d'Amo species, the roebuck, the horse, the stag, 
the Irish elk, the Certus Polignactis, foimd also at Mont Perrier, 
France, C. verticomis, and C. carnuiorum, the latter also found 
in Pliocene strata of St. Prest, France. In the fluvio-marine 
series have been found the Cyclas omnica and the Paludina 
mfirgtMia, a species of mollusc still found in the South of France, 
but no longer inhabiting the British Isles. 

Above the forest bed and fluvio-marine series comes the well- 
known unstratified Norwich boulder till, containing immense 
blocks 6 or 8 feet in diameter, many of which must have come 
from Scandinavia, and above the unstratified till are a series of 
contorted beds of sand and gravel. This series may be con- 
sidered to represent a period of intense glaciation. Above this 
again comes the middle drift of Mr. Searles Wood, junior, 
yielding shells which indicate, as is now generally admitted, 
a comparatively mild condition of climate. Upon this middle 
drift lies the upper boulder clay, which is well developed in 
South Norfolk and Suflblk, and which is of unmistakable 
glacial origin. Newer than all these are the Mundesley fresh- 
water beds, which lie in a hollow denuded out of the foregoing 



INTER-GLACIAL PERIODS. »5i 

series. In this formation a black peaty deposit containing 
seeds of plants, insects, shells, and scales and bones of fishes, 
has been found, all indicating a mild and temperate condition 
of climate. Among the shells there is, as in the forest bed, 
the Paludina marginata. And that an arctic condition of 
things in England followed is believed by Mr. Fisher and 
others, on the evidence of the " Trail " described by the former 
observer. 

Cave and River Deposits, — Evidence of the existence of warm 
periods during the glacial epoch is derived from a class of facts 
which have long been regarded by geologists as very puzzling, 
namely, the occurrence of mollusca and mammalia of a southern 
type associated in England and on the continent with those of 
an extremely arctic character. For example j Cyrena fluminalis 
is a shell which does not live at present in any European river, 
but inhabits the Nile and parts of Asia, especially Cashmere. 
Unio iiitoralis, extinct in Britain, is still abundant in the 
Loire; Paludina marginata does not exist in this country. 
These shells of a southern type have been found in post-tertiary 
deposits at Gray's Thurrock, in Essex ; in the valley of the 
Ouse, near Bedford ; and at Hoxne, in Suffolk, associated with 
a Hippopotamus closely allied to that now inhabiting the Nile, 
and E/ejj/ias antiquus, an animal remarkable for its southern 
range. Amongst other forms of a southern type which have 
been met with in the cave and river deposits, are the spotted 
hyaena from Africa, an animal, says Mr. Dawkins, identical, 
except in size, with the cave hyaena, the African elephant 
{E, Africanus)y and the Elephas meridionaiis, the great beaver 
(Trogont/ierium) , the cave hyaena {Hyc^na spelcea), the cave lion 
{Felis leo, var. spelcea), the lynx (Felis Ij/nx), the sabre-toothed 
tiger [Machairodus laiidens), the rhinoceros (Rhinoceros mega- 
rhinus and R. leptorhinus). But the most extraordinary thing is 
that along with these, associated in the same beds, have been 
found the remains of such animals of an arctic type as the 
glutton {Guk iuscus), the ermine {Mustela enninea), the reindeer 
{Cernis tarandus), the musk-ox or musk-sheep {Oribos mo'fcfiaim), 



152 CLIMATE AND TIME. 

the aurochs (Bison prisciis), the woolly rhinoceros {Rhinoceros 
tichorhintis), the mammoth (Elephaa primigenitts), and others of a 
like character. According to Mr. Boyd Dawkins, these southern 
animals extended as far north as Yorkshire in England, and the 
northern animals as far south as the latitude of the Alps and 
Pyrenees.* 

The Explanation of the Difficulty. — As an explanation of these 
puzzling phenomena, I suggested, in the Philosophical Maga- 
zine for November, 1868, that these southern animals lived in 
our island during the warm periods of the glacial epoch, while 
the northern animals lived during the cold periods. This view 
I am happy to find has lately been supported by Sir John 
Lubbock ; further, Mr. James Geikie, in his " Great Ice Age," 
and also in the Geological Magazine, has entered so fully into 
the subject and brought forward such a body of evidence in 
support of it, that, in all probability, it will, ere long, be 
generally accepted. The only objection which has been ad- 
vanced, so far as I am aware, deserving of serious consideration, 
is that by Mr. Boyd Dawkins, who holds that if these migra- 
tions had been secular instead of seasonal, as is supposed by Sir 
Charles Lyell and himself, the arctic and southern animals 
would now be found in separate deposits. It is perfectly true 
that if there had been only one cold and one warm period, each 
of geologically immense duration, the remains might, of course, 
be expected to have been foimd in separate beds ; but when we 
consider that the glacial epoch consisted of a long succession oj 
alternate cold and warm periods, of not more than ten or twelve 
thousand years each, we can hardly expect that in the river 
deposits belonging to this long cycle we should be able to dis- 
tinguish the deposits of the cold periods from those of the warm. 

Shell Beds. — ^Evidence of warm inter-glacial periods may be 
justly inferred from the presence of shells of a southern tj'pe 
which have been foimd in glacial beds, of which some illustra- 
tions follow. 

In the southern parts of Norway, from the present sea-level 

• Quart. Journ. Geol. Soc, xxviii., p. 435. 



INTER-GLACIAL PERIODS. 153 

up to 600 feet, are found glacial BhcU beds, similar to those of 
Scotland. In these beds Trochua magus, Tapes decussata, and 
Pholas Candida have been found, shells which are distributed 
between the Mediterranean and the sliorcs of England, but no 
longer live round the coasts of Norway. 

At Capellbacken, near Udevalla, in Sweden, there is an 
extensive bed of shells 20 to 30 feet in thickness. This forma- 
tion has been described by Mr. Giivyn Jeffreys.* It consists of 
several distinct layers, apparently representing many epochs 
and conditions. Its shells are of a highly arctic character, and 
several of the species have not been found living south of the 
arctic circle. But the remarkable circumstance is that it 
contains Cj/prcBa lurida, a Mediterranean shell, which Mr. 
Jeffreys, after some hesitation, believed to belong to the bed. 
Again, at Lillehcrstchagen, a short distance from Capellbacken, 
another extensive deposit is exposed. " Here the upper layer/* 
aays Mr. Jeffreys, " gives a singular result. Mixed with the 
universal Trophon clathratus (which is a high northern species, 
and found living only within the arctic circle) are many shells 
of a southern type, such are Ostrea edulis, Tapes pullastra, 
Corbula gibba, and Aporrhais pes-pelicani. 

At Kempsey, near Worcester, a shell bed is described by Sir 
B. Murchison in his "Silurian System" (p. 533), in which 
Bulla ampulla and a species of Oliva, shells of a southern type, 
have been found. 

A case somewhat similar to the above is recorded by the 
Bev. Mr. Grosskoy as having been met with in Scotland at the 
Eyles of Bute. " Among the Clyde beds, I have found," he 
says, **a layer containing shells, in which those of a more 
southern type appear to exist in greater profiision and perfec- 
tion than even in our present seas. It is an open question," 
he continues, "whether our climate was not slightly warmer 
than it is now between the glacial epoch and the present 

day."t 

♦ Brit. Aasoo. Report, 1868. 

t Trans. Glaagow Nat. Hut. Soc , vol. L, p. U^ 



«54 CLIMATE AND TIME. 

In a glacial bed near Greenock, Mr. A. Bell found the fry of 
living Mediterranean forms, viz., ConuB Mediterraneus and 
Cardita trapezia. 

Although deposits containing shells of a temperate or of a 
southern type in glacial beds have not been often recorded, it 
by no means follows that such deposits are actually of rare 
occurrence. That glacial beds should contain deposits indicat- 
ing a temperate or a warm condition of climate is a thing so 
contrary to all preconceived opinions regarding the sequence of 
events during the glacial epoch, that most geologists, were 
they to meet with a shell of a southern type in one of those 
beds, would instantly come to the conclusion that its occurrence 
there was purely accidental, and would pay no special attention 
to the matter. 

Evidence derived from ** Borings.'* — With the view of ascer- 
taining if additional light would be cast on the sequence of 
events, during the formation of the boulder clay, by an exami- 
nation of the journals of bores made through a great depth of 
surface deposits, I collected, during the summer of 1867, 
about two hundred and fifty such records, put down in all 
parts of the mining districts of Scotland. An examination of 
these bores shows most conclusively that the opinion that the 
boulder clay, or lower till, is one great undivided formation, 
is wholly erroneous. 

These two hundred and fifty bores represent a total thick- 
ness of 21,348 feet, giving 86 feet as the mean thickness of the 
deposits passed through. Twenty of these have one boulder clay, 
with beds of stratified sand or gravel beneath the clay ; twenty- 
five have tico boulder clays, with stratified beds of sand and 
gravel between ; ten have ^//ree boulder clays ; one has four boul- 
der clays ; two have^r^ boulder clays ; and no one has fewer than 
six separate masses of boulder clay, with stratified beds of sand 
and gravel between ; sixteen have two or three separate boulder 
clays, differing altogether in colour and hardness, without any 
stratified beds between. We have, therefore, out of two hun- 
dred and fifty bores, seventy-five of them representing a con- 



INTER'GLACIAL PERIODS. «5S 

dition of things wholly different from that exhibited to the 
geologist in ordinary sections. 

The full details of the character of the deposits passed 
through by these bores, and their bearing on the history of the 
glacial epoch, have been given by Mr. James Bennie, in an 
interesting paper read before the Glasgow Geological Society,* 
to which I would refer all those interested in the subject of 
surface geology. 

The evidence afforded by these bores of the existence of 
warm inter- glacial periods will, however, fall to be considered 
in a subsequent chapter, t 

Another important and unexpected result obtained from 
these bores to which we shall have occasion to refer, was the 
evidence which they afforded of a Continental Period. 

Striated Pavements, — It has been sometimes observed that in 
horizontal sections of the boulder clay, the stones and boulders 
are all striated in one uniform direction, and this has been 
effected over the original markings on the boulders. It has 
been inferred from this that a pause of long duration must 
have taken place in the formation of the boulder clay, during 
which the ice disappeared and the clay became hardened into a 
solid mass. After which the old condition of things returned, 
glaciers again appeared, passed over the surface of the hardened 
clay with its imbedded boulders, and ground it down in the 
same way as they had formerly done the solid rocks underneath 
the clay. 

An instance of striated pavements in .the boulder clay was 
observed by Mr. Robert Chambers in a cliff between Portobello 
and Fisherrow. At several places a narrow train of blocks was 
observed crossing the line of the beach, somewhat like a quay 
or mole, but not more than a foot above the general level. All 
the blocks had flat sides uppermost, and all the flat sides tcere 
striated in the same direction as that of the rocky surface through- 

* Trans, of the Geol. Soc. of Glasgow, toI. iii., p. 133. See also " Greftt loe 
Age,*' chaps, xii. and ziii. 
t Chap. XXIX. 



•56 CLIMATE AND TIME. 

out tlie country. A similar instance was also observed between 
lioith and Portobello. " There is, in short," says Mr. Cham- 
bers, ** a surface of the boulder clay, deep down in the entire 
bed, which, to appearance, has been in precisely the same 
circumstances as the fast rock surface below had previously 
been. It has had in its turn to sustain the weight and abrad- 
ing force of the glacial agent, in whatever form it was applied ; 
and the additional deposits of the boulder clay left over this 
surface may be presumed to have been formed by the agent on 
that occasion/** 

Several cases of a similar character were observed by Mr. 
James Smith, of Jordanhill, on the beach at Row, and on the 
shore of the Gareloch.t Between Dunbar and Cockbumspath, 
Professor Geikie found along the beach, for a space of 30 
or 40 square yards, numbers of large blocks of limestone with 
flattened upper sides, imbedded in a stiff red clay, and all 
striated in one direction. On the shores of the Solway he 
found another example.* 

The cases of striated pavements recorded are, however, not 
very numerous. But this by no means shows that they are of 
rare occurrence in the boulder clay. These pavements, of 
course, are to bo found only in the interior of the mass, and 
even there they can only be seen along a horizontal section. 
But sections of this kind are rarely to be met with, for river 
channels, quarries, railway cuttings, and other excavations of a 
similar character which usually lay open the boulder clay, 
exhibit vertical sections only. It is therefore only alonj^ the 
sea-shore, as Professor Geikie remarks, where the surface of the 
clay has been worn away by the action of the waves, that oppor- 
tunities have hitherto been presented to the geologist for ob- 
serving them. 

There can be little doubt that durinpr the warm periods of 
the glacial epoch our island would be clothed with a luxuriant 

♦ Edin. New Phil. Jonm., vol. liv., p. 272. 

t "Newer Pliocene Geology," p. 129. John Gray & Co., GLuigow. 

X ** Glacial Drift of Scotland," p. 67. 



INTER-GLACIAL PERIODS. 257 

flora. At the end of a cold period, when the ice had disap- 
pearedy the whole face of the country would bo covered over to 
a considerable depth with a confused mass of stones and 
boulder clay. A surface thus wholly destitute of every seed 
and germ would probably remain for years without vegetation. 
But through course of time life would begin to appear, and 
during the thousands of years of perpetual summer which 
would follow, the soil, uncongenial as it no doubt must ha^e 
been, would bo forced to sustain a luxuriant vegetation. But 
although this was the case, we need not wonder that now 
scarcely a single vestige of it remains ; for when the ice sheet 
again crept over the island everything animate and inanimate 
would be ground down to powder. We are certain that 
prior to the glacial epoch our island must have been covered 
with life and vegetation. But not a single vestige of these are 
now to be found ; no, not even of the very soil on which the 
vegetation grew. The solid rock itself upon which the soil lay 
has been ground down to mud by the ice sheet, and, to a 
large extent, as Professor Geikie remarks, swept away into the 
adjoining seas.* It is now even more difficult to find a trace 
of the ancient soil under the boulder clay than it is to find 
remains of the soU of the warm periods in that clay. As 
regards Scotland, cases of old land surfaces under the boulder 
clav are as seldom recorded as cases of old land surfaces in it. 
In so far as geology is concerned, there is as much evidence to 
show that our island was clothed with vegetation during the 
glacial epoch as there is that it was so clothed prior to that 
epoch. 

• *' Glacial Drift of Scotland/* p. 12. 



CHAPTER XVL 

WARH INTEB-01ACIAL PERIODS IN ARCTIC RROION9. 

Cold Periods best marked in Temperate, and Warm PeriodR in Arctic, Regions. 
— State of Arctic Regions during Glacial Period. — fiiiects of Removiil of Io« 
from Arctio Regions. — Ocean-Currenta ; Influence on Arctic Climate.— 
Reason why Remains of Inter-gladal Period are rare in Arctic Regions. 
— Remains of Ancient Forests in Banks's Land, Prince Patrick's Island, &o. 
— Opinions of Sir R. Murchison, Captain 0»bom, and Professor Haughton. 
—Tree dug up by Sir E. Belcher in lat, 75* N. 

In the temperate regions the cold periods of tho glacial 
epoch would be far more marked than the warm inter-glacial 
periods. The condition of things which prevailed during the 
cold periods would differ far more widely from that which now 
prevails than would the condition of things during the warm 
periods. But as regards the polar regions the reverse would be 
the case ; there the warm inter-glacial periods would be far 
more marked than the cold periods. The condition of things 
prevailing in those regions during the warm periods would be 
in strongest contrast to what now obtains, but this would not 
hold true in reference to the cold periods ; for during the 
latter, matters there would be pretty much the same as at 
present, only a good deal more severe. The reason of this may 
be seen from what has already been stated in Chapter IV. ; but 
as it is a point of considerable importance in order to a proper 
understanding of the physical state of things prevailing in 
polar regions during the glacial epoch, I shall consider this 
piirt of the subject more fully. 

During the cold periods, our island, and nearly all places 
in the northern temperate regions down to about the same 
latitude, would be covered with snow and ice, and all animal 
and vegetable life within the glaciated area would to a great 



INTER-GLACIAL PERIODS. 259 

9xtent be destroyed. The presence of the ice would of itself, 
for reasons already explained, lower the mean annual tempera- 
ture to near the freezing-point. The summers, notwithstand- 
ing the proximity of the sun, would not be warm, on the con- 
trary their temperature would rise little above the freezing- 
point. An excess of evaporation would no doubt take place, 
owing to the increase in the intensity of the sun's rays, but 
this result would only tend to increase the snowfall.* 

During the warm periods our country and the regions under 
consideration would experience conditions not differing much 
from those of the present, but the climate would probably bo 
somewhat wanner and more equable. The proximity of the 
sun during winter would prevent snow from falling. The 
summers, 'owing to the greater distance of the sim, would 
probably be somewhat colder than they are now. But the loss 
of heat during summer would be to a large extent compensated 
for by two causes to which we must here refer. (1.) The much 
greater amount of heat conveyed by ocean-currents than at 
present. (2.) Our summers are now cooled to a considerable 
extent by cold aerial currents from the ice-covered regions of 
the north. But during the period in question there would be 
little or no ice in arctic regions, consequently the winds would 
be comparatively warm, whatever direction they came from. 

Let us next direct our attention to the state of things in the 
arctic regions during the glacial epoch. At present Greenland 
and other parts of the arctic regions occupied by land are 
almost wholly covered with ice, and as a consequence nearly 
destitute of vegetable life. During the cold periods of the 
glacial epoch the quantity of snow falling would doubtless be 
greater and the ice thicker, but as regards organic life, matters 
would not probably be much worse than they are at present. 
In fact, so far as Greenland and the antarctic continent are con- 
cerned, they are about as destitute of plant life as they can be. 
Although an increase in the thickness of the arctic ice would 
not greatly alter the present state of matters in those regionsi 

♦ See Chapter IV. 



i6o CLIMATE AND TIME. 

yet what a transformation would ensue upon the disappearance 
of the ice ! This would not only raise the summer temperature 
some twenty degrees or so, but would afford the necessary 
conditions for the existence of abundant animal and plant life. 
The severity of the climate of Greenland is due to a very con- 
siderable extent, as we have already seen, to the presence of ice. 
Get rid of the permanent ice, and the temperature of the 
country, cceteris paribus, would instantly rise. That Greenland 
should ever have enjoyed a temperate climate, capable of sup- 
porting abundant vegetation, has often been matter of astonish- 
ment, but this wonder diminishes when we reflect that during 
the warm periods it would be in the arctic regions that the 
greatest heating effect would take place, this being due mainly 
to the transference of nearly all the warm inter- tropical waters 
to one hemisphere. 

It has been shown in Chapter II. that the heating effects at 
present resulting from the transference of heat by ocean-cur- 
rents increase as we approach the poles. As a consequence of 
this it follows that during the warm periods, when the quantity 
of warm water transferred would be nearly doubled, the inci^ease 
of heat resulting from this cause would itself increase as the warm 
pole was approached. This effect, combined with the shortness 
of the winter in perihelion and the nearness of the sun during 
that season, would prevent the accumulation of snow. During 
summer, the sun, it is true, would be at a much greater distance 
from the earth than at present, but it must be borne in mind 
that for a period of three months the quantity of heat received 
from the sun at the north pole would be greater than that 
received at the equator. Consequently, after the winter's snow 
was melted, this great amount of heat would go to raise the 
temperature, and the arctic summer could not be otherwise 
than hot. It is not hot at present, but this, be it observed, is 
because of the presence of the ice. When we take all these 
facts into consideration we need not be surprised that Green- 
land once enjoyed a condition of climate totally different from 
that which now obtains in that region. 




INTER-GLACIAL PERIODS. 261 

It is, therefore, in the arctic and antarctic regions where we 
ought to find the most marked and decided evidence of warm 
inter-glacial periods. And doubtless such evidence would be 
abimdantly forthcoming had these regions not been subjected to 
such intense denudation since the glacial epoch, and were so large 
a portion of the land not still buried beneath an icy covering, 
and therefore beyond the geologist's reach. Only on islands 
and such outlying places as are not shrouded in snow and ice 
can we hope to meet with any trace of the warm periods of the 
glacial epoch : and we may now proceed to consider what relics 
of these warm periods have actually been discovered in arctic 
regions. 

Evidence of Warm Periods in Arctic Regions. — The fact that 
stumps, &c., of full-grown trees have been found in places 
where at present nothing is to be met with but fields of^ snow 
and ice, and where the mean annual temperature scarcely rises 
above the zero of the Fahrenheit thermometer, is good evidence 
to show that the climate of the arctic regions was once much 
warmer than now. The remains of an ancient forest were 
discovered by Captain McClure, in Banks's Land, in latitude 
74° 48'. He found a great accumulation of trees, from the sea- 
level to an elevation of upwards of 300 feet. " I entered a 
ravine," says Captain McClure, " some miles inland, and found 
the north side of it, for a depth of 40 feet from the surface, 
composed of one mass of wood similar to what I had before 
seen." ♦ In the ra\'ine he observed a tree protruding about 
8 feet, and 3 feet in circumference. And he further states 
that, ^^ From the perfect state of the hark, and the position 
of the trees so far from the sea, there can be but little doubt 
that they grew originally in the country." A cone of one of 
these fir-trees was brought home, and was found to belong 
apparently to the genus Abies y resembling A, (Pinm) alba. 

In Prince Patrick's Island, in latitude 76° 12' N., longitude 
122° W., near the head of Walker Inlet, and a considerable 
distance in the interior in one of the ravines, a tree protruding 

♦ *« Discovery of the North- Wc«t Pasaage," p. 218. 



i6a CLIMATE AND TIME. 

about 10 feet from a bank was discoyered by Lieutenant 
Mecham. It proved to be 4 feet in circumference. In its 
neighbourhood several others were seen, all of them similar to 
some he had found at Cape Manning ; each of them measured 
4 feet round and 30 feet in length. The carpenter stated 
that the trees resembled larch. Lieutenant Mecham, from 
their appearance and position, concluded that they must have 
grown in the country.* 

Trees under similar conditions were also foimd by Lieutenant 
Pim on Prince Patrick's Island, and by Captain Parry on Mel- 
ville Island, all considerably above the present sea-level and at 
a distance from the shore. On the coast of New Siberia, 
Lieutenant Anjou found a cliff of clay containing stems of trees 
still capable of being used for fuel. 

"This remarkable phenomenon," says Captain Osborn, "opens 
a vast field for conjecture, and the imagination becomes be- 
wildered in trying to realise that period of the world's history 
when the absence of ice and a milder climate allowed forest 
trees to grow in a region where now the ground-willow and 
dwarf-birch have to struggle for existence." 

Sir Roderick Murchison came to the conclusion that all those 
trees were drifted to their present position when the islands 
of the arctic archipelago were submerged. But it was the 
difficulty of accoimting for the growth of trees in such a region 
which led him to adopt this hypothesis. His argument is this : 
"If we imagine," he says, "that the timber found in those 
latitudes grew on the spot we should be driven to adopt the 
anomalous hypothesis that, notwithstanding physical relations 
of land and water similar to those which now prevail, trees of 
large size grew on such terra firma within a few degrees of the 
north pole! — a supposition which I consider to be wholly 
incompatible with the data in our possession, and at variance 
with the laws of the isothermal lines." t This reasoning of 
Sir Roderick's may be quite correct, on the supposition that 

• " Voyage of the BetoluU;' p. 294. 

t Quart. Journ. Geol. Soc., vol. xi., p. 640. 




INTER-GLACIAL PERIODS. ibi 

eLonges of climate are due to changes in the distribution of sea 
and land, as advocated by Sir Charles Lyell But these diffi- 
culties disappear if we adopt the views advocated in the fore- 
going chapters. As Captain Osbom has pointed out, however, 
Sir Roderick's hypothesis leaves the real difficulty untouched. 
** A very diffisrent climate," he says, "must then have existed 
in those regions to allow driftwood so perfect as to retain its 
bark to reach such great distances ; and perhaps it may be 
argued that if that sea was sufficiently clear of ice to allow such 
timber to drift unscathed to Prince Patrick's Land, that that 
very absence of a frozen aea would allow fir-trees to grow in a soil 
naturally fertile J^ * 

As has been already stated, all who have seen those trees in 
arctic regions agree in thinking that they grew in situ. And 
Professor Haughton, in his excellent account of the arctic 
archipelago appended to McClintock's " Narrative of Arctic 
Discoveries," after a careful examination of the entire evidence 
on the subject, is distinctly of the same opinion; while the 
recent researches of Professor Heer put it beyond doubt that 
the drift theory must be abandoned. 

Undoubtedly the arctic archipelago was submerged to an 
extent that could have admitted of those trees being floated to 
their present positions. This, as we shall see, follows from 
theory ; but submergence, without a warmer condition of climate, 
would not enable trees to reach those regions with their bark 
entire. 

But in reality we are not left to theorise on the subject, for 
we have a well-authenticated case of one of those trees being 
got by Captain Belcher standing erect in the position in which 
it grew. It was found immediately to the northward of the 
narrow strait opening into Wellington Sound, in lat. 75° 32' N. 
long. 92° W., and about a mile and a half inland. The tree 
was dug up out of the frozen ground, and along with it a 
portion of the soil which was immediately in contact with the 
roots. The whole was packed in canvas and brought to 
• ** McClure's North- Weat Paasago,** p. 214. Second Edition, 



264 CLIMATE AND TIME 

England. Near to the spot several knolls of peat mosses about 
nine inches in depth were found, containing the bones of the 
lemming in great numbers. The tree in question was examined 
by Sir William Hooker, who gave the following report con- 
cerning it, which bears out strongly the fact of its having grown 
in 9itu. 

" The piece of wood brought by Sir Edward Belcher from 
the shores of Wellington Channel belongs to a species of pine, 
probably to the Pinus {Abies) alhUy the most northern conifer. 
The structure of the wood of the specimen brought home differs 
remarkably in its anatomical character from that of any other 
conifer with which I am acquainted. Each concentric ring (or 
annual growth) consists of two zones of tissue ; one, the outer, 
that towards the circumference, is broader, of a pale colour, 
and consists of ordinary tubes of fibres of wood, marked with 
discs common to all coniferae. These discs are usually opposite 
one another when more than one row of them occur in the 
direction of the length of the fibre ; and, what is very unusual, 
present radiating lines from the central depression to the cir- 
cumference. Secondly, the inner zone of each annual ring of 
wood is narrower, of a dark colour, and formed of more slender 
woody fibres, with thicker walls in proportion to their diameter. 
These tubes have few or no discs upon them, but are covered 
with spiral striae, giving the appearance of each tube being 
formed of a twisted band. The above characters prevail in all 
parts of the wood, but are slightly modified in diflercnt rings. 
Thus the outer zone is broader in some than in others, the disc- 
bearing fibres of the outer zone are sometimes faintly marked 
with spiral striae, and the spirally marked fibres of the inner 
zone sometimes bear discs. These appearances suggest the 
annual recurrence of some special cause that shall thus modify 
the first and last formed fibres of each year's deposit, so that 
that first formed may differ in amount as well as in kind from 
that last formed; and the peculiar conditions of an arctic 
climate appear to ajQTord an adequate solution. The inner, or 
firat'formed zone, must bo regarded as imperfectly developed, 



INTER-GLACIAL PERIODS. abs 

being deposited at a season when the functions of the plant are 
very intermittently exercised, and when a few short hours of 
sunshine are daily succeeded by many of extreme cold. As 
the season advances the sun's heat and light are continuous 
during the greater part of the twenty-four hours, and the 
newly formed wood fibres are hence more perfectly developed, 
they are much longer, present no signs of stria), but are studded 
with discs of a more highly organized structure than are usual 
in the natural order to which this tree belongs." * 

Another circumstance which shows that the tree had grown 
where it was found is the fact that in digging up the roots 
portions of the leaves were obtained. It may also be mentioned 
that near this place was found an old river channel cut deeply 
into the rock, which, at some remote period, when the climate 
must have been less rigorous than at present, had been occupied 
by a river of considerable size. 

Now, it is evident that if a tree could have grown at "Wel- 
lington Sound, there is no reason why one might not have 
grown at Banks's Land, or at Prince Patrick's Island. And, if 
the climatic condition of the country would allow one tree to 
grow, it would equally as well allow a hxmdred, a thousand, or 
a whole forest. If this, then, be the case, Sir Roderick's objec- 
tion to the theory of growth in situ falls to the ground. 

Another circumstance which favours the idea that those 
trees grew during the glacial epoch is the fact that although 
they are recent, geologically speaking, and belong to the drift 
series, yet they are, historically speaking, very old. The wood, 
though not fossilized, is so hardened and changed by age that 
it will scarcely bum. 

• <' British Association Heport for 1855/' p. 381. "The Last of the Aiekifl 
Voyages,*' vol. L, p. 381. 



CHAPTER XVn. 

rOBMER OLAaAL EPOCHS. KBASOK OP THS IMPERFECTION OP 

GEOLOGICAL RECORDS IN REPERENCE TO THEM. 

Two Rensons why so litUe is known of Glacial Epochs. — ^Evidence of Glaciation 
to be found on Land-surfaces. — ^Where are all our ancient L'md-surfaces P^ 
The stratified Kr>ck8 consist of a Series of old Sea-bottoms. — Transformation 
of a Land-surface into a Sea-bottf^m obliterates all Traces of Glaciation. — 
Why so little remains of the Boulder Cla>-8 of former Glacial Epochs. — 
Records of the Glacial Epoch are fitst disappearing— Icebergs do not striate 
the Sea-bottom. — Mr. Campbell's Obsenrations on the Coast of Labrador. — 
Amount of Material tmnsported by Icebergs much exaggerated. — Mr. 
PHckard on thoGUrial Phenomena of Labrador. — Boulder Clay the Product 
of Land-ice. — Palaont^dogical Evidence. — Paucity of Life characteristic of 
a Glacial Period. — Warm Periods belter represented by Organic Remains 
than cold. — Why the Climate of the Tertiary Period was supposed to be 
warmer than the present. — ilr. James Geikie on the Defects of Palssonto- 
logical Evidence. — Cv^nclasion. 

Tiro Reasons why so little is knoicn offonmr Glacial Epochs, — 
If the glacial epoch resulted from the causes discussed in the 
foregoing chapters, then such epochs must have frequently 
supervened. We may, therefore, now proceed to consider what 
evidence there is for the former occurrence of excessive condi- 
tions of climate during previous geological ages. When we 
begin our inquiry, however, we soon find that the facts which 
have been recorded as evidence in favour of the action of ice in 
former geological epochs are very scanty indeed. Two obviouB 
reasons for this may be given, namely, (1) The imperfection 
of the geological records themselves, and (2) the little attention 
hitherto p.iid toward researches of this kind. The notion, once 
80 prevalent, that the climate of our earth was much warmer in 
th efflri icr geological ages than it is now, and that it has ever 
gradually becoming cooler, was wholly at variance 




FORMER GLACIAL EPOCHS, 267 

«rith the idea of former ice-periods. And this conviction of the 
d priori improbability of cold periods having obtained during 
PalaDozoic and Mesozoic ages tended to prevent due attention 
being paid to such facts as seemed to bear upon the subject. But 
OUT limited knowledge of former glacial epochs must no doubt 
be attributed chiefly to the actual imperfection of the geologi- 
cal records. So g^at is this imperfection that the mere absence 
of direct geological evidence cannot reasonably be regarded 
as sufficient proof that the conclusions derived from astrono- 
mical and physical considerations regarding former ice-periods 
are improbable. Nor is this all. The geological records of 
ancient glacial conditions are not only imperfect, but, as I shall 
endeavour to show, this imperfection follows as a natural conse^ 
quencefrom the principles of geology itself There are not merely 
so many blanks or gaps in the records, but a reason exists in 
the very nature of geological evidence why such breaks in the 
record might reasonably be expected to occur. 

Evidence of Glaciation to be found chuff/ on Land-surfaces. — 
It is on a land-surface that the principal traces of the action of 
ice during a glacial epoch are left, for it is there that the stones 
are chiefly striated, the rocks ground down, and the boulder 
clay formed. But where are all our ancient land-surfaces P 
They are not to be found. The total thickness of the stratified 
rocks of Great Britain is, according to Professor Ramsay, nearly 
fourteen miles. But from the top to the bottom of this enor- 
mous pile of deposits there is hardly a single land-surface to be 
detected. True patches of old land-surfaces of a local character 
exist, such, for example, as the dirt-beds of Portland ; but, 
with the exception of coal-seams, every general formation from 
top to bottom has been accumulated under water, and none but 
the under-clays ever existed as a /an^f- surface. And it is here, in 
such a formation, that the geologist has to collect all his in- 
formation regarding the existence of former glacial epochs. 
The entire stratified rocks of the globe, with the exception of 
the coal-beds and under-clays (in neither of which would one 
expect to find traces of ice-action), consist almost entirely of a 



i68 CUM ATE AND TIME, 

teries of old sea-bo f tome, with here and there an occasional fi*eah« 
water deposit. Bearing this in mind, what is the sort of 
evidence which we can now hope to find in these old sea- 
bottoms of the existence of former ice-periods P 

Every geologist of course admits that the stratified rocks are 
not old land-surfaces, but a series of old sea-bottoms formed out 
of the accumulated material derived from the degradation of 
primeval land-surfaces. And it is true that all land-surfaces 
once existed as sea-bottoms; but the stratified rocks consist 
of a series of old sea- bottoms which never were land-surfaces. 
Many of them no doubt have been repeatedly above the sea- 
level, and may once have possessed land-surfaces ; but these, 
with the exception of the imder-clays of the various coal 
measures, the dirt-beds of Portland, and one or two more 
patches, have all been denuded away. The importiint bearing 
which this consideration has on the nature of the evidence 
which we can now expect to find of the existence of former 
glacial epochs has certainly been very much overlooked. 

If we examine the matter fully we shall be led to conclude 
that the tram/ormation of a lanci-sur/ace into a sea- bottom will 
probably completely obliterate every trace of glaciation which 
that land-surface may once have presented. We cannot, for 
example, expect to meet with polished and striated stones 
belonging to a former land glaciation ; for such stones are not 
carried down bodily and unchanged by our rivers and deposited 
in the sea. They become broken up by subaerial agencies into 
gravel, sand, and clay, and in this condition are transported 
seawards. Nor even if we supposed it posi<iblc that the stones 
and boulders derived from a mass of till could be carried down 
to sea by river-action, could we at the same time fail to admit 
that such stones would be deprived of all their ico-markinge, 

and become water-worn and rounded on the wav.* 

• 

• Mr, James Gkikie informs me that the {iTviit accumulations of gravel which 
occur so abundantly in the low grounds of Switzurlaud, and which are, undoubt- 
edly, merely the rc-arranged materials originally brought down from the Alps 
as tiU and as moraines by the glacii^rs during thn glacial ep<»c-h, rart^ly or never 
yiojda single scratched or glaciated btuue. The action ut the riveiu ebcapiug 




FORMER GLACIAL EPOCHS. 269 

Nor can we expect to find boulder clay among the stratified 
rocks, for boulder clay is not carried down as such and deposited 
in the sea, but under the influence of the denuding agents 
becomes broken up into soft mud, clay, sand, and gravel, as it 
is gradually peeled off the land and swept seawards. Patches 
of boulder clay may have been now and again forced into the 
sea by ice and eventually become covered up ; but such cases 
are wholly exceptional, and their absence in any formation 
cannot fairly be adduced as a proof that that fonnation does 
not belong to a glacial period. 

The only evidence of the existence of land-ice during former 
periods which we can reasonably expect to meet with in 
the stratified rocks, consists of erratic blocks which may have 
been transported by icebergs and dropped into the sea. Bat 
unless the glaciers of such epochs reached the sea, we could 
not possibly possess even this evidence. Traces in the stratified 
rocks of the effects of land-ice during former epochs must, in 
the very nature of things, be rare indeed. The only sort of 
evidence which, as a general rule, we may expect to detect, is 
the presence of largo erratic blocks imbedded in strata which 
£rom their constitution have evidently been formed in still 
water. But this is quite enough ; for it proves the existence 
of ice at the time the strata were being deposited as conclusively 
as though we saw the ice floating with the blocks upon it. This 
sort of evidence, when found in low latitudes, ought to be 
received as conclusive of the existence of former glacial epochs ; 
and, no doubt, would have been so received had it not been for 
the idea that, if these blocks had been transported by ice, there 
ought in addition to have been found striated stones, boulder 
clay, and other indications of the agency of land-ice. 

Of course all erratics are not necessarily transported by 

from the m'ltinpf ice has succeeded in obliterating all tr;ice of striie. It is the 
■limp, ho siiys, with the heaps of gravel and sand in the lower grounds of Sweden 
and Norway, Scotland and Ireland. These deposits are evidently in the first 
place merely the materials carried down by the swollen rivers that issued from 
the gnidually malting ice-fields and glaciers. The stones of tl»e gravel derived 
from the denK>liti"n of montines and till, have lost all their stiise and htxjome in 
most c>i«*es well water-worn and rounded. 



170 CLIMATE AND TIME. 

masses of ice broken from the terminal front of glaciers. The 
" ice foot," formed by the freezing of the sea along the coasts 
of the higher latitudes of Greenland, carries seawards immense 
quantities of blocks and debris. And again stones and boulders 
are frequently frozen into river-ice, and when the ice breaks 
up in spring are swept out to sea, and may be carried some little 
distance before they are dropped. But both these cases can 
occur only in regions where the winters are excessive ; nor is 
it at all likely that such ice-rafts will succeed in making a long 
voyage. If, therefore, we coidd assure ourselves that the 
erratics occasionally met with in certain old geological forma - 
tions in low latitudes were really transported from the land by 
an ice-foot or a raft of river-ice, we should be forced to con- 
clude that very severe climatic conditions must have obtained 
in such latitudes at the time the erratics were dispersed. 

The reason why we now have, comparatively speaking, so 
little direct evidence of the existence of former glacial periods 
vriYL be more forcibly impressed upon the mind, if we reflect on 
how difficult it would be in a million or so of years hence to 
find any trace of what we now call the glacial epoch. The 
striated stones would by that time be all, or nearly all, disinte- 
grated, and the till washed away and deposited in the bottom 
of the sea as stratified sands and clays. And when those 
became consolidated into rock and were raised into dry land, 
the only evidence that we should probably then have that there 
ever had been a glacial epoch would be the presence of largo 
blocks of the older rocks, which would be found imbedded in 
the upraised formation. We could only infer that there had 
been ice at work from the fact that by no other known agency 
could we conceive such blocks to have been transported and 
dropped in a still sea. 

Probably few geologists believe that during the Middle 
Eocene and the Upper Miocene periods our country passed 
through a condition of glaciation as severe as it has done 
during the Post-pliocene period ; yet when we examine the 
subject carefully, we find that there is actually no just p^round 



FORMER GLACIAL EPOCHS. 271 

to conclude that it has not. For, in all probability, throughout 
the strata to be eventually formed out of the destruction of the 
now existing land-surfaces, evidence of ice- action will be as 
scarce as in Eocene or Miocene strata. 

If the stratified rocks forming the earth's crust consisted of 
a series of old land-surfaces instead (as they actually do) of a 
series of old sea-bottoms, then probably traces of many glacial 
periods might be detected. 

Nearly all the evidence which we have regarding the glacial 
epoch has been derived from what we find on the now existing 
land-surfaces of the globe. But probably not a vestige of this 
will exist in the stratified beds of future ages, formed out of the 
destruction of the present land-surfaces. Even the very arctic 
shell-beds themselves, which have afibrded to the geologist 
such clear proofs of a frozen sea during the glacial epoch, will 
not be found in those stratified rocks ; for they must suffer 
destruction along with everything else which now exists above 
the sea-level. There is probably not a single reHc of the glacial 
epoch which has ever been seen by the eye of man that will be 
treasured up in the stratified rocks of future ages. Nothing 
that docs not lie buried in the deeper recesses of the ocean will 
escape complete disintegration and appear imbedded in those 
formations. It is only those objects which lie in our existing 
^sea-bottoms that will remain as monuments of the glacial epoch 
of the Post-tertiary period. And, moreover, it will only be 
those portions of the sea-bottoms that may happen to be 
upraised into dry land that will be available to the geologist of 
future ages. The point to be determined now is this : — Is it 
probable that the geologist of the future mil find in the rocks 
formed out of the now existing sea-bottoms more evidence of a 
glacial epoch during Post-tertiary times than we now do of one 
during f sag, the Miocene, the Eocene, or the Permian period? 
Unless this can be proved to be the case, we have no ground 
whatever to conclude that the cold periods of the Miocene, 
Eocene, and Permian periods were not as severe as that of the 
glacial epoch This is evident, for the only relics which now 

13 



171 CLIMATE AND TIME. 

remain of the glacial epochs of those periods are simply what 
happened to be protected in the then existing sea-bottoms. 
Every vestige that lay on the land would in all probability be 
destroyed by subaerial agency and carried into the sea in a 
sedimentary form. But before we can determine whether or 
not there is more evidence of the glacial epoch in our now 
existing sea-bottoms than there is of former glacicd epochs in 
the stratified rocks (which are in reality the sea-bottoms 
belonging to ancient epochs), we must first ascertain what is 
the nature of those marks of glaciation which are to be found 
in a sea-bottom. 

Icebergs do not striate the Sea-bottotn, — TVe know that the 
rocky face of the country was ground down and striated during 
the glacial epoch ; and this is now generally believed to have 
been done by land-ice. But we have no direct evidence that 
the floor of the ocean, beyond where it may have been covered 
with land-ice, was striated. Beyond the limits of the land-ice 
it could be striated only by means of icebergs. But do icebergs 
striate the rocky bed of the ocean P Are they adapted for such 
work P It seems to be often assumed that they are. But I 
have been totally unable to find any rational grounds for such 
a belief. Clean ice can have but little or no erosive power, and 
never could scratch a rock. To do this it must have grinding 
materials in the form of sand, mud, or stones. But the bottoms 
of icebergs are devoid of all such materials. Icebergs carry the 
grinding materials on their backs, not on their bottoms. No 
doubt, when the iceberg is launched into the deep, great masses 
of sand, mud, and stones will be adhering to its bottom. But 
no sooner is the berg immersed, than a melting process com- 
mences at its sides and lower surface in contact with the water ; 
and the consequence is, the materials adhering to the lower 
surface soon drop off and sink to the bottom of the sea. The 
iceberg, divested of these materials, can now do very little harm 
to the rocky sea-bottom over which it floats. It is true that an 
iceberg moving with a velocity of a few miles an hour, if it 
oame in contact with the sea-bottom, would, by the mere force 




FORMER GLACIAL EPOCHS. zjs 

of concuBsion, tear up loose and disjointed rocks, and hurl some 
of the loose materials to a distance ; but it would do but little 
in the way of grinding down the rock against which it struck. 
But even supposing the bottom of the iceberg were properly 
shod with the necessary grinding materials, still it would be 
but a very inefficient grinding agent ; for a /loafing iceberg 
would not be in contact with the sea-bottom. And if it were 
in contact with the sea-bottom, it would soon become stranded 
and, of course, motionless, and under such conditions could pro- 
duce no effect. 

It is perfectly true that although the bottom of the berg may 
be devoid of grinding materials, yet these may be foimd lying 
on the surface of the submarine rock over which the ice moves. 
But it must be borne in mind that the same current which will 
move the icebergs over the surface of the rock will move the 
sand, mud, and other materials over it also; so that the 
markings effected by the ice would in all probability be erased 
by the current. In the deep recesses of the ocean the water 
has been found to have but little or no motion. But icebergs 
always follow the path of currents; and it is very evident 
that at the comparatively small depth of a thousand feet or so 
reached by icebergs the motion of the water will be considerable ; 
and the continual shifting of the small particles of the mud and 
sand will in all probability efface the markings which may be 
made now and again by a passing berg. 

Much has been said regarding the superiority of icebergs as 
grinding and striating agents in consequence of the great 
velocity of their motion in comparison with that of land-ice. 
But it must be remembered that it is while the iceberg is floating, 
and before it touches the rock, that it possesses high velocity. 
When the iceberg runs aground, its motion is suddenly arrested 
or greatly reduced. But if the iceberg advancing upon a 
sloping sea-bottom is raised up so as to exert great pressure, it 
will on this account be the more suddenly arrested, the motion 
will be slow, and the distance passed over short, before the berg 
becomes stranded. If it exerts but little pressure on the sea- 



*74 CLIMATE AND TIME. 

bottom, it may retain a considerable amount of motion and 
adyanee to a considerable distance before it is brought to a 
stand; but, exerting little pressure, it can perform but little 
work. Land-ice moves slowly, but then it exerts enormous 
pressure. A glacier 1,000 feet in thickness has a pressure on 
its rocky bed equal to about 25 tons on the square foot ; but an 
iceberg a mile in thickness, forced up on a sloping sea-bottom 
to an elevation of 20 feet (and this is perhaps more than any 
ocean- current could effect), would only exert a pressure of about 
half a ton on the square foot, or about l-50th part of the pressure 
of the glacier 1,000 feet in thickness. A great deal has been 
said about the erosive and crushing power of icebergs of enor- 
mous thickness, as if their thickness gave them any additional 
pressure. An iceberg 100 feet in thickness will exert just as 
much pressure as one a mile in thickness. The pressure of an 
iceberg is not like that of a glacier, in proportion to its thick- 
ness, but to the height to which it is raised out of the water. 
An iceberg 100 feet in thickness raised 10 feet will exert 
exactly the same pressure as one a mile in thickness raised to 
an equal height. 

To be an efficient grinding agent, steadiness of motion, as 
well as pressure, is essential. A rolling or rocking motion is 
ill-adapted for grinding down and striating a rock. A steady 
rubbing motion under pressure is the thing required. But an 
iceberg is not only deficient in pressure, but also deficient in 
steadiness of motion. When an iceberg moving with consider- 
able velocity comes on an elevated portion of the sea-bottom, it 
does not move steadily onwards over the rock, imless the pres- 
sure of the berg on the rock be trifling. The resistance being 
entirely at the bottom of the iceberg, its momentum, combined 
with the pressure of the current, applied wholly above the 
point of resistance, tends to make the berg bend forward, and in 
some cases upset (when it is of a cubical form). The momentum 
of the moving berg, instead of being applied in forcing it over 
the rock against which it comes in contact, is probably all con- 
sumed in work against gravitation in raising the berg upon its 



FORMER GLACIAL EPOCHS. 275 

front edge. After the momentum is consumed, unless the berg 
be completely upset, it will fall back under the force of gravita- 
tion to its original position. But the momentum which it 
acquires from gravitation in falling backwards carries it beyond 
its position of repose in an opposite direction. It will thua 
continue to rock backwards and forwards until the friction of 
the water brings it to rest. The momentum of the berg, 
instead of being applied to the work of grinding and striat- 
ing the sea-bottom, will chiefly be consumed in heat in the 
agitation of the water. But if the berg does advance, it will 
do so with a rocking unsteady motion, which, as Mr. Couthouy • 
and Professor Danaf observe, will tend rather to obliterate 
striations than produce them. 

A floating berg moves with great steadiness; but a berg 
that has run aground cannot advance with a steady motion. 
If the rock over which the berg moves oiffers little resistance, it 
may do so ; but in such a case the berg could produce but little 
efiect on the rock. 

Dr. Sutherland, who has had good opportunities to witness the 
effects of icebergs, makes some most judicious remarks on the 
subject. " It will be well " he says, " to bear in mind that 
when an iceberg touches the ground^ if that ground he hard and 
resistmg, it must conie to a standi and the propelling power con- 
tinuing, a slight leaning over in the water, or yielding motion 
of the whole ma«s, may compensate readily for being so sud- 
denly arrested. If, however, the ground be soft, so as not to 
arrest the motion of the iceberg at once, a moraine will be the 
result ; but the moraine thus raised will tend to bring it to a 
stand.'' t 

There is another cause referred to by Professor Dana, which, 
to a great extent, must prevent the iceberg from having an 
opportunity of striating the sea-bottom, even though it were 
otherwise well adapted for so doing. It is this : the bed of the 

• Report on Icebergs, read before tbe Association of Amarican Geologists, 
Silliman's Journal, vol. xliii., p. 163 (1842). 
t " Manual of Geology," p. 677. 
X Quart. Journ. Geol. Soc., voL ix.. p. 806. 



176 CLIMATE AND TIME. 

ocean in the track of icebergs mart be poretiy mncli coTored with 
rtones and rdbbiah dropped from the melting bergs. And this 
mass of rubbish will tend to protect the rock.* 

If icebergs cannot be shown d priori, tram mechanical con* 
siderationsy to be well adapted for stiiating the sea^bottom, one 
would naturally expect, from the confident way in which it is 
asserted that they are so adapted, that the fact has been at least 
established by actual observation. But, strange as it may 
appear, we seem to haye little or no proof that icebergs actually 
striate the bed of the ocean. This can be proved from the direct 
testimony of the advocates of the iceberg theory themselves. 

We shall take the testimony of Mr. Campbell, the author of 
two well-known works in defence of the iceberg theory, viz., 
"Frost and Fire,*' and "A Short American Tramp.'* Mr. 
Campbell went in the fall of the year 1864 to the coast of 
Labrador, the Straits of Belle Isle, and the Gulf of St. Lawrence, 
fbr the express purpose of witnessing the effects of icebergs, 
and testing the theory which he had formed, that the ice- 
markings of the glacial epoch were caused by floating ice and 
not by land-ice, as is now generally believed. 

The following is the result of his observations on the coast of 
Labrador. 

Hanly Harbour, Strait of Belle Isle :— " The water is 37° F. 
in July. ... As fast as one island of ice grounds and bursts, 
another takes its place; and in winter the whole strait is 
blocked up by a mass which swings bodily up and down, 
grating along the bottom at all depths. . • . Examined the 
beaches and rocks at the water-line, especially in sounds. 
Found the rocks ground smooth, but not striated, in the sounds ** 
(Short American Tramp, pp. 68, 107). 

Cape Charles and Battle Harbour: — ''But though these 
harbours are all frozen every winter, the rocks at tfie water-line 
mre not striated'* (p. 68). 

At St. Francis Harbour : — '' The water-line is much rubbed, 
■mooth, but not striated** (p. 72). 

• Dtna's ** Maniial of Geology," p. 677. 



FORMER GLACIAL EPOCHS. 277 

Cape Bluff: — "Watched the rocks with a telescope, and 
failed to make out strue ant/where ; but the water-line is every- 
where rubbed smooth " (p. 75). 

Seal Islands: — **I^0 8tri(e are to be seen at the land-wash in 
these sounds or on open sea-coasts near the present water-line*^ 
(p. 76). 

He only mentions haying here found striations in the three 
following places along the entire coast of Labrador visited by 
him ; and in regard to two of these, it seems very doubtful that 
the markings were made by modem icebergs. 

Murray's Harbour : — " This harbour was blocked up with 
ice on the 20th of July. The water-line is rubbed, and in sotne 
places striated" (p. 69). 

Pack Island : — " The water-line in a narrow sound was 
polished and striated in the direction of the sound, about 
N.N.W. This seems to be fresh work done by heavy ice 
drifting from Sandwich Bay ; but, on th^ other hand, stages with 
their legs i?i the sea, and resting on these very rocks, are not swept 
away by the ice " (p. 96). If these markings were modem, why 
did not the " heavy ice " remove the small fir poles supporting 
the fishing-stages P 

Red Bay : — " Landed haK-dressed, and found some strisB 
perfectly fresh at the water-level, but weathered out a short 
di&tsLnce inland** (p. 107). The striations " inland " coidd not 
have been made by modem icebergs ; and it does not follow 
that because the markings at the water-level were not weathered 
they were produced by modem ice. 

These are the evidences which he found that icebergs striate 
rocks, on a coast of which he says that, during the year he 
visited it, " the winter-drift was one vast solid raft of floes and 
bergs more than 150 miles wide, and perhaps 3,000 feet thick 
it spots, driven by a whole current bodily over one definite 
course, year after year, since this land was found " (p. 85). 

But Mr. Campbell himself freely admits that the floating 
ice which comes aground along the shores does not produce 
stria), " It is sufficiently evident," he says, " that glacial %Mm 



Mjt CLIMATE AND TIME. 

mt not produced by thin hay ice '* (p. 76). And in '' Frost and 
Fire,'' voL ii., p. 237, li6 states tliat, '* £rom a oarefiil examina- 
tion of the water-line at many spots, it appears that baj-ios 
grinds rocks, btU does not produce etriation" 

" It is impossible/' he oontinues, ** to got at rocks over wkich 
keayy icebergs now move ; but a mass 150 miles wide, perhaps 
8,000 feet thick in some parts, and moving at the rate of a 
mile an hour, or more, appears to be an engine amply sufficient 
to account for striss on rising rocks/' And in '^ American 
Tramp,'' p. 76, he says, ** strim must be made in docp water by 
the large masses which seem to pursue the even tenor of their 
way in the steady current which flows down the coast." 

Mr. Campbell, from a careful examination of the sea-bottom 
along the coast, finds that the small icebergs do not produce 
striee, but the large ones, which move over rocks impossible to 
be got at, " must " produce them. They " appear " to be amply 
sufiicient to do so. If the smaller bergs cannot striate the sea- 
bottom, why must the larger ones do so P There is no reason 
why the smaller bergs should not move as swiftly and exert as 
much pressure on the sea-bottom as the larger ones. And even 
supposing that they did not, one would expect that the light 
bergs would effect on a smaUer scale what the heavy ones would 
do on a larger. 

I have no doubt that when Mr. Campbell visited Labrador 
he expected to find the sea-coast under the water-line striated 
by means of icebergs, and was probably not a little surprised te 
find that it actually was not. And I have no doubt that were 
the sea-bottom in the tracks of the large icebergs elevated into 
view, he would find to his surprise that it was free fi*om stria- 
tions also. 

So far as observation is concerned, we have no grounds from 
what Mr. Campbell witnessed to conclude that icebergs striate 
the sea-bottom. 

The testimony of Dr. Sutherland, who has had opportunities 
of seeing the effects of icebergs in arctic regions, leads us to 
the same conclusion. <' Except," he says, '' from the evidence 



FORMER GLACIAL EPOCHS. 279 

afforded by plants and animals at the bottom, we baye no meam 
whatever to ascertain the effect produced by icebergs upon the 
rocks.* In the Malegat and Waigat I have seen whole clus- 
ters of these floating islands, drawing from 100 to 250 
fathoms, moving to and fro with every return and recession of 
the tides. I looked very earnestly for grooves and scratches 
left by icebergs and glaciers in the rocks, but fJways failed to 
discover any." t 

We shall now see whether river- ice actually produces stria- 
tions or not. If floating ice under any form can striate rocks, 
one would expect that it ought to be done by river-ice, seeing 
that such ice is obliged to follow one narrow definite track. 

St. John's River, New Brunswick : — **This river," says Mr. 
Campbell, '' is obstructed by ice during five months of the year. 
When the ice goes, there is wild work on the bank. Arrived 
at St. John, drove to the suspension-bridge. ... At this spot, 
if anywhere in the worlds river-ice ought to produce striation. 
The whole drainage of a wide basin and one of the strongest 
tides in the world, here work continually in one rock-groove ; 
and in winter this water-power is armed with heavy ice. There 
are no strice about the water-line." + 

River St. Lawrence : — " In winter the power of ice-floats 
driven by water-power is tremendous. The river freezes and 
packs ice till the flow of water is obstructed. The rock-pass 
at Quebec is like the Narrows at St. John's, Newfoundland. 
The whole pass, about a mile wide, was paved with great 
broken slabs and roxmd boulders of worn ice as big as small 
stacks, piled and tossed, and heaped and scattered upon the 

level water below and frozen solid This kind of ice 

does NOT produce sf nation at the water-margin at Quebec. At 
Montreal, when the river * goes,' the ice goes with it with a 

vengeance The piers are not yet striated by river-ice at 

Montreal The rocks at the high-water level have no 

trace of glacial striaB The rock at Ottawa is rubbed by 

♦ Quart. Journ. Oeol. 80c., vol. ix., p. 806. f " Jonrnal," voL i., p. 8S. 

i ** Short American Tramp,'* pp. 16S, 174. 



z8o CLIMATE AND TIME. 

riT0r-ioe erery Bpring, and alhcay% m om Hredion^ but U i$ not 
gtriated, . • • • The sorfacea are all mbbed smooth, and the 
edges of broken beds are rounded where exposed to the ice ; but 
there are no stria" * 

When Sir Oharles Lyell visited the St. Lawrence in 1842, at 
Quebec he went along with Colonel Codrington ''and searched 
carefully below the city in the channel of the St. Lawrence, at 
low water, near the shore, for the signs of glacial action at the 
precise point where the chief pressure and friction of packed 
ice are exerted every year/' but found none. 

" At the bridge above the Falls of Montmorenci, over which 
a large quantity of ice passes every year, the gneiss is polished, 
and kept perfectly free from lichens, but not more so than rocks 
similarly situated at water&lls in Scotland. In none of these 
places were any long straight grooves observable." t 

The only thing in the shape of modem ice-markings which 
he seems to have met with in North America was a few straight 
furrows half an inch broad in soft sandstone, at the base of a 
cliff at Cape Blomidon in the Bay of Fundy, at a place where 
during the preceding winter " packed " ice 15 feet thick had 
been pushed along when the tide rose over the sandstone 
ledges.} 

The very fact that a geologist so eminent as Sir Charles Lyell, 
after having twice visited North America, and searched specially 
for modem ice-markings, was able to find only two or three 
scratches, upon a soft sandstone rock, which ho could reasonably 
attribute to floating ice, ought to have aroused the suspicion of 
the advocates of the iceberg theory that they had really formed 
too extravagant notions regarding the potency of flouting ice 
as a striating agent. 

There is no reason to believe that the grooves and markings 
noticed by H. Weibye and others on the Scandinavian coast 
and other parts of northern Europe were made by icebergs. 

* ''Short American Tramp,*' pp. 239—241. 
t •«TraTel8 m North Amerios,'^Tol. iL, p. 137. 
X Hud., ToL 11., p. 174« 



FORMER GLACIAL EPOCHS. i8i 

Professor Geikie has clearly shown, from the character and 
direction of the markings, that they are the production of land- 
ice.* If the floating ice of the St. Lawrence and the icebergs 
of Labrador are unable to striate and groove the rocks, it is not 
likely that those of northern Europe will be able to do so. 

It will not do for the advocates of the iceberg theory to as- 
sume, as they have hitherto done, that, as a matter of course, 
the sea-bottom is being striated and grooved by means of ice- 
bergs. They must prove tliat. They must either show that, as 
a matter of fact, icebergs are actually efficient agents in striating 
the sea-bottom, or prove from mechanical principles that they 
must be so. The question must be settled either by observation 
or by reason ; mere opinion will not do. 

The Amount of Material transported by Icebergs much exag- 
gerated, — The transporting of boulders and rubbish, and not 
the grinding and striating of rocks, is evidently the proper 
function of the iceberg. But even in this respect I fear too 
much has been attributed to it. 

In reading the details of voyages in the arctic regions one 
cannot help feeling surprised how seldom reference is made to 
stones and rubbish being seen on icebergs. Arctic voyagers, 
like other people, when they are alluding to the geological 
effects of icebergs, speak of enormous quantities of stones being 
transported by them ; but in reading the details of their voy- 
ages, the impression conveyed is that icebergs with stones and 
blocks of rock upon them are the exceptions. The greater 
portion of the narratives of voyages in arctic regions consists 
of interesting and detailed accounts of the voyager's adven- 
tures among the ice. The general appearance of the icebergs, 
their shape, their size, their height, their colour, are all noticed ; 
but rarely is mention made of stones being seen. That the 
greater number of icebergs have no stones or rubbish on them 
is borne out by the positive evidence of geologists who have 
had opportunities of seeing icebergs. 

Mr. Campbell says: — "It is remarkable that up to this 

* Proceedings of the Boyal Socioty of Edinburgh, Session 1866—66, p. 687. 



i8a CLIMATE AND TIME. 

time welia^ only seen a few doubtful stones on bergs which wa 
have passed. .... Though no bergs with stones on Ihem or m 
fkem have been approached during this Tojagei many on board 

the Ariel ha^e been dose to bergs hearily laden A man 

who has had some experience of ice has never eeen a etone on a 
berg in these latitudes. Oaptain Anderson, of the Eurqpa, who 
is a geologist, has never eeen a ehne on a berg in crossing the 
Atlantic. No etonee tpere etearfy eeen on this trip,*** Captain 
Sir James Anderson (who has long boen familiar with geology, 
has spent a considerable part of his life on the Atlantic, and has 
been accustomed to Tiew the iceberg as a geologist as well as a 
seaman) has never seen a stone on an iceberg in the Atlantic. 
This is rather a significant fact. 

Sir Charles Lyell states that, when passing icebergs on the 
Atlantic, he " was most anxious to ascertain whether there was 
any mud, stones, or fragments of rocks on any one of these 
floating masses ; but after examining about forty of them with- 
out perceiving any signs of frozen matter, I left the deck when 
it was growing dusk.^'f After he had gone below, one was 
said to be seen with something like stones upon it. The 
captain and officers of the ship assured him that they had 
never eeen a stone upon a berg. 

The following extract from Mr. Packard's '' Memoir on the 
Olacial Phenomena of Labrador and Maine," will show how 
little is effected by the great masses of floating ice on the 
Labrador coast either in the way of grinding and striating the 
rocks, or of transporting stones, clay, and other materials. 

"Upon this coast, which during the summer of 1864 was 
lined with a belt of floe-ice and bergs probably two hundred 
miles broad, and which extended from the Gulf of St, Lawrence 
at Belles Amours to the arctic seas, this immense body of 
floating ice seemed directly to produce but little alteration in its 
physical features. If we were to ascribe the grooving and 
polishing of rocks to the action of floating ice-floes and bergs, 

• ••Short Americui Tramp," pp. 77, 81, 111. 
t <« Second Vint." vol. ii., p S67. 




FORMER GLACIAL EPOCHS. 183 

how is it that the present shores far ahove (600), and at least 
250 feet below, the water-line are often jagged and angular, 
though constantly stopping the course of masses of ice impelled 
four to six nules an hour by the joint action of tides, cur- 
rents, and winds ? No boulders, or gravel, or mud were seen 
upon any of the bergs or masses of shore-ice. They had 
dropped all burdens of this nature nearer their points of 
detachment in the high arctic regions." .... 

" This huge area of floating ice, embracing so many thou- 
sands of square miles, was of greater extent, and remained 
longer upon the coast, in 1864, than for forty years previous. 
It was not only pressed upon the coast by the normal action of 
the Labrador and Greenland currents, which, in consequence of 
the rotatory motion of the earth, tended to force the ice in a 
south-westerly direction, but the presence of the ice qiused the 
constant passage of cooler currents of air from the sea over the 
ice upon the heated land, giving rise during the present season 
to a constant succession of north-easterly winds from March 
\mtil early in August, which further served to crowd the ice 
into every harbour and recess upon the coast. It was the 
universal complaint of the inhabitants that the easterly winds 
were more prevalent, and the ice * held * later in the harbours 
this year than for many seasons previous. Thus the fisheries 
were nearly a failure, and vegetation greatly retarded in its 
development. But so far as polishing and striating the rocks, 
depositing drift material, and thus modifying the contour of the 
surface of the present coast, this modem mass of bergs and float- 
ing ice effected comparatively little. Single icebergs, when 
small enough, entered the harbours, and there stranding, soon 
pounded to pieces upon the rocks, melted, and disappeared. From 
Cape Harrison, in lat. 55°, to Caribo Island, was an interrupted 
line of bergs stranded in 80 to 100 or more fathoms, often miles 
apart, while others passed to the seaward down by the eastern 
coast of Newfoundland, or through the Straits of Belle Isle."* 

Boulder Clay the Product of Land-ice. — There is still 

• " Memoirs of Boston Society of Natural History," vol. i. (1867), p. 228. 



<t4 CLIMATE AND TIME. 

Mofliar point mmiwiirij wifli kdwig» Id vUdi ire nml 
dbde^ riz^ the opinioii that gmfe anaM of flie boulder 
d^ of the glacial epoch weiie ainned fioni the dioppiagii 
of iec b cf g* . If booUer day it at pnaent heiiig accmaii- 
lafted in this numiier^ then traoea of the boulder day deponta 
of former epocha might be expected to ooenr. It ia perfecU j 
o bn o na that unttraiified boolder cky coold not hare been 
fiinned in this way. Stonea, gmTel, sand, clar, and mod, the 
ingredients of boolder chiy, tumbled all together from the back 
of an iceberg, coold not sink to the bottom of the sea without 
aapaxating. The stones would reach the bottom first, thai the 
grsfd, then the sand, then the day, and last of all the mud, 
and the whole would settle down in a stratified form. But, 
besides, how could the ela^ be derived from icebergs ? Ice- 
bergs deriTe their materials from the land before they are 
launched into the deep, and while they are in the form of land- 
ice* The materials which are found on the backs of icebergs 
are what fell upon the ice from mountain tops and crags pro- 
jecting above the ice. Icebergs are chiefly derived from con- 
tinental ice, such as that of Ghreenland, where the whole country 
is buried under one continuous mass, with only a lofty moun- 
tain peak here and there rising above the surfa^. And this is 
no doubt the chief reason why so few icebergs have stones 
upon their backs. The continental ice of Greenland is not, 
like the glaciers of the Alps, covered with loose stones. 
Dr. Robert Brown informs me that no moraine matter has 
ever been seen on the inland ice of Greenland. It is per- 
fectly plain that day does not fall upon the ice. What falls 
upon the ice is stones, blocks of rocks, and the loose debris. 
day and mud we know, from the accounts given by arctic 
ToyagerSy are sometimes washed down upon the coast-ice ; but 
oertainly very little of either can possibly get upon an iceberg. 
Aretio vpyagers sometimes speak of seeing clay and mud upon 
beigs; but it ia probable that if they had been near enough 
Aaj would have found that what they took for clay and mud 
mmmnAj dnst and mbbisk. 




FORMER GLACIAL EPOCHS. a8s 

Undoubtedly the boulder clay of many places bears unmis- 
takable evidence of having been formed under water ; but it 
does not on that accoimt follow that it was formed from the 
droppings of icebergs. The &ct that the boulder clay in every 
case « chiefly composed of materials derived from the country on 
which the clay lies, proves that it was not formed from matter 
transported by icebergs. The clay, no doubt, contains stones 
and boulders belonging to other countries, which in some cases 
may have been transported by icebergs ; but the clay itself has 
not come from another coimtry. But if the clay itself has been 
derived from the coimtry on which it lies, then it is absurd to 
suppose that it was deposited from icebergs. The clay and 
materials which are found on icebergs are derived from the 
land on which the iceberg is formed ; but to suppose that ice- 
bergs, after floating about upon the ocean, should always return 
to the country which gave them birth, and there deposit their 
loads, is rather an extravagant supposition. 

From the facts and considerations adduced we are, I would 
venture to presume, warranted to conclude that, with the 
exception of what may have been produced by land-ice, very 
little in the shape of boulder clay or striated rocks belonging 
to the glacial epoch lies buried imder the ocean — and that when 
the now existing land-surfaces are all denuded, probably scarcely 
a trace of the glacial epoch will then be found, except the huge 
blocks that were transported by icebergs and dropped into the 
sea. It is therefore probable that we have as much evidence of 
the existence of a glacial epoch during former periods as the 
geologists of future ages wUl have of the existence of a glacial 
epoch during the Post-tertiary period, and that consequently 
we are not warranted in concluding that the glacial epoch was 
something unique in the geological history of our globe. 

Pakeoiitological Evidence. — ^It might be thought that if glacial 
epochs have been nimierous, we ought to have abundance of 
palaeontological evidence of their existence. I do not know 
if this necessarily follows. Let us take the glacial epoch itself 
for example, which is quite a modem affair. Here we do not 



286 CLIMATE AND TIME. 

require to go and searcli in the bottom of the sea for the 
eyidence of its existence ; for we have the surface of the land 
in almost identically the same state in which it was when the 
ice left it, with the boulder clay and all the wreck of the ice 
lying upon it. But what geologist, with all these materials before 
him, would be able to find out from palaeontological evidence 
alone that there had been such an epoch P He might search 
the whole, but would not be able to find fossil evidence from 
which he could warrantably infer that the country had ever 
been covered with ice. We have evidence in the fossils of the 
Crag and other deposits of the existence of a colder condition 
of climate prior to the true glacial period, and in the shell-beds 
of the Clyde and other places of a similar state of matters after 
the great ice-sheets had vanished away. But in regard to the 
period of the true boulder clay or till, when the coxmtry was 
enveloped in ice, palaeontology has almost nothing whatever to 
tell us. "Whatever may be the cause," says Sir Charles 
Lyell, " the fact is certain that over large areas in Scotland, 
[reland, and Wales, I might add throughout the northern 
hemisphere on both sides of the Atlantic, the stratified 
drift of the glacial period is very commonly devoid of 
fossils.*' ♦ 

In the " flysch " of the Eocene of the Alps, to which we shall 
have occasion to refer in the next chapter, in which the huge 
blocks are found which prove the existence of ice-action during 
that period, few or no fossils have been found. So devoid of 
organic remains is that formation, that it is only from its 
position, says Sir Charles, that it is known to belong to the 
middle or ** nummulitic " portion of the great Eocene series. 
Again, in the conglomerates at Turin, belonging to the Upper 
Miocene period, in which the angular blocks of limestone are 
found which prove that during that period Alpine glaciers 
reached the sea-level in the latitude of Italy, not a single 
organic remain has been found. It would seem that an extreme 
paucity of organic life is a characteristic of a glacial period, 

• " Antiqaily of Man," p. 26S Third Edition. 



FORMER GLACIAL EPOCHS. iSj 

whicli warrants us in concluding that the absence of organic 
remains in any formation otherwise indicative of a cold climate 
cannot be regarded as sufficient evidence that that formation 
does not belong to a cold period. 

In the last chapter it was shown why so little evidence of 
the warm periods of the glacial epoch is now forthcoming. 
The remains of the faunae oxidi floras of those periods were nearly 
wholly destroyed and swept into the adjoining seas by the ice- 
sheet that covered the land. It is upon the present land- 
surface that we find the chief evidence of the last glacial epoch, 
but the traces of the warm periods of that epoch are hardly now 
to be met with in that position since they have nearly all been 
obliterated or carried into the sea. 

In regard to former glacial epochs, however, ice-marked 
rocks, scratched stones, moraines, till, &c., no longer exist ; the 
land-surfaces of those old times have been utterly swept away. 
The only evidence, therefore, of such ancient glacial epochs, 
that we can hope to detect, must be sought for in the deposits 
that were laid down upon the sea-bottom ; where also we may 
expect to find traces of the warm periods that alternated during 
such epochs with glacial conditions. It is plain, moreover, that 
the palaeontological evidence in favour of warm periods will 
always be the most abundant and satisfactory. 

Judging from geological evidence alone, we naturally con- 
clude that, as a general rule, the climate of former periods was 
somewhat warmer than it is at the present day. It is from 
fossil remains that the geologist principally forms his estimate 
of the character of the climate during any period. Now, in 
regard to fossil remains, the warm periods will always be fer 
better represented than the cold ; for we find that, as a general 
rule, those formations which geologists are inclined to believe indicate 
a cold condition of climate are remurkahly devoid of fossil remains. 
If a geologist does not keep this principle in view, he will be 
very apt to form a wrong estimate of the general character of 
the climate of a period of such enormous length as say the 
Tertiary. 



i88 CLIMATE AND TIME. 

Suppose that tlie presently existing sea-bottoms, whicli liave 
been forming since the commencement of the glacial epocb, were 
to become consolidated into rock and thereafter to be elevated 
into dry land, we should then have a formation which might be 
properly designated the Post-pliocene. It would represent the 
time which has elapsed from the beginning of the glacial epoch 
to the present day. Suppose one to be called upon as a geologist 
to determine from that formation what was the general character 
of the climate during the period in question, what would pro- 
bably be the conclusion at which he would arrive ? He would 
probably find here and there patches of boulder clay containing 
striated and ice-worn stones. Now and again he would meet 
with bones of the mammoth and the reindeer, and shells of an 
arctic type. He would likewise stumble upon huge blocks of 
the older rocks imbedded in the formation, from which he would 
infer the existence of icebergs and glaciers reaching the sea- 
level. But, on the whole, he would perceive that the greater 
portion of the fossil remains met with in this formation implied 
a warm and temperate condition of climate. At the lower part 
of the formation, corresponding to the time of the true boulder- 
clay, there would be such a scarcity of organic remains that he 
would probably feel at a loss to say whether the climate at that 
time was cold or hot. But if the intense cold of the glacial 
epoch was not continuous, but broken up by intervening warm 
periods during which the ice, to a considerable extent at least, 
disappeared for a long period of time (and there are few geo- 
logists who have properly studied the subject who will positively 
deny that such was the case), then the country would no doubt 
during those warm periods possess an abundance of plant and 
animal life. It is quite true that we may almost search in vain 
on the present land-surface for the organic remains which 
belonged to those inter-glacial periods ; for they were nearly 
all swept away by the ice which followed. But no doubt in the 
deep recesses of the ocean, buried under hundreds of feet of sand, 
mud, clay, and gravel, lie midtitudes of the plants and animala 
which then flourished on the land, and were carried down by 




FORMER GLACIAL EPOCHS. 289 

rivers into the sea. And along with these lie the skeletons, 
shells, and other exuviaD of the creatures which flourished in 
the warm seas of those periods. Now looking at the great 
abundance of fossils indicative of warm and genial conditions 
which the lower portions of this formation would contain, the 
geologist might be in danger of inferring that the earlier part 
of the Post-pliocene period was a warmer period, whereas we, at 
the present day, looking at the matter from a diflerent stand- 
point, declare that part to have been characterized by cold or 
glacial conditions. No doubt, if the beds formed during the 
cold periods of the glucial epoch coidd be distinguished from 
those formed during the warm periods, the fossil remains of the 
one would indicate a cold condition of climate, and those of the 
other a warm condition ; but still, taking the entire epoch as a 
whole, the percentage of fossil remains indicative of a warm 
condition would probably so much exceed that indicative of a 
cold condition, that we should come to the conclusion that the 
character of the climate, as a whole, during the epoch in ques- 
tion was warm and equable. 

As geologists we have, as a rule, no means of arriving at a 
knowledge of the character of the climate of any given period 
but through an examination of the sea-bottoms belonging to 
that period ; for these contain all the evidence upon the sub- 
ject. But unless we exercise caution, we shall be very apt, in 
judging of the climate of such a period, to fall into the same 
error that we have just now seen one might naturally fall into 
were he called upon to determine the character of the climate 
during the glacial epoch from the nature of the organic remains 
which lie buried in our adjoining seas. On this point Mr. J. 
Geikie's observations are so appropriate, that I cannot do better 
than introduce them here. " When we are dealing," says this 
writer, " with formations so far removed from us in time, and 
in which the animal and plant remains depart so widely from 
existing forms of life, we can hardly expect to derive much aid 
from the fossils in our attempts to detect traces of cold climatio 
conditions. The arctic shells in our Post-tertiary clays are 



t90 CUMATE AND TIME. 

ocmvinoing pn)0& of the former existence in our ktitade of a 
■ereore climate ; but when we go ao &r back as Palseosoio 
ages^ we have no such dear evidence to guide us. All that 
palfiDontologists can say regarding the fossils belonging to these 
old times is simply this, that they seem to indicate, generally 
speaking, mild, temperate^ or genial, and even sometimes 
tropical, conditions of climate. Many of the fossils, indeed, if 
we are to reason from analogy at all, could not possibly have 
lived in cold seas. But^ for aught that we know, there may have 
been alternations of climate during the deposition of each par- 
ticular formation ; and these changes may be marked by the 
presence or absence, or by the greater or less abundant develop- 
ment, of certain organisms at various horizons in the strat&. 
Notwithstanding all that has been done, our knowledge of the 
natural history of these ancient seas is still very imperfect ; 
and therefore, in the present state of our information, we are not 
entitled to argue, from the general aspect of the fossils in our 
older formations, that the temperature of the ancient seas was 
never other than mild and geniaL''* 

Conchision. — From what has already been stated it will, I 
trust, be apparent that, assuming glacial epochs during past 
geological ages to have been as numerous and as severe as the 
Secular theory demands, still it would be unreasonable to expect 
to meet with abundant traces of them. The imperfection of the 
geological record is such that we ought not to be astonished 
that so few relics of former ice ages have come down to us. It 
will also be apparent that the palsBontological evidence of a 
warm condition of climate having obtained during any par 
ticular age, is no proof that a glacial epoch did not also super- 
vene during the same cycle of time. Indeed it is quite the 
reverse ; for the warm conditions of which we have proof may 
indicate merely the existence of an inter-glacial period. Fur- 
thermore, if the Secular theory of changes of climate be ad- 
mitted, then evidence of a warm condition of climate having 

• **Qgmi Ice Age/' p. 612. 



FORMER GLACIAL EPOCHS. 



291 



preyailed in arctic regions during any past geological age may 
be regarded as presumptive proof of the existence of a glacial 
epoclL ; that is to say, of an epoch during which cold and warm 
conditions of climate alternated. Keeping these considerations 
in view, we shaU now proceed to examine briefly what 
eyidence we at present have of the former existence of glacial 
epochs. 



CHAPTER XVni. 

FORMER GLACIAL EPOCHS; GEOLOGICAL EVIDENCB 07. 

Chmkbriui Oooglomerate of ItlAy and North-west of Sootland. — loe-action in 
Aynhire and Wigtownshire dnzing Silurian Period.— Silurian lamestonea 
in Arctio Begions. — ^Professor Bamsay on Ice-action during Old Red Sand- 
stone Period. — ^Wann Climate in AroUo Begions during Old Bed Sandstone 
Period. — Professor Geikie and Mr. James Choikie on a Qiacial CSonglomerate 
of Lower Carboniferous Age. — Professor Huughton and Professor Dawson on 
Evidence of Ice-action during CoelI Period. — Mr. W. T. Blanford on Glaci- 
ation in India during Carboniferous Period. — Carboniferous Formations of 
Arctio Begions. — Professor Bamsay on Pennian Glaciers. — Permian Con- 

flomerate in Arran. — ^Professor Hull on Boulder Clay of Pennian Age. — 
^ermian Boulder Cla^ of Natal. — Oolitic Boulder Conglomerate in Suther- 
laodshire. — ^Warm Clunate in North Greenland during Oolitic Period.—Mr. 
Godwin- Austen on Ice-aotion during Cretaceous Period. — Glacial Conglo- 
merates of Eocene Age in the Alps. — M. Gastaldi on the Ice- transported 
Limestone Blocks of the Superga. — ProfeMor ileer on the Climate of North 
Greenland daring Miocene Period. 



CAMBRIAN PERIOD. 

Inland of lahy. — Good evidence of ice-action has been ob- 
served by Mr. iTames Thomson, F.G.S.,* in strata which he 
believes to be of Cambrian age. At Port Askaig, Island of 
Islay, below a precipitous cliff of qiiartzite 70 feet in height, 
there is a mass of arenaceous talcose schist containing fragments 
of granite, some angular, but most of them rounded, and of all 
sizes, from mere particles to large boiddcrs. As there is no 
granite in the island from which these boulders could have been 
derived, he justly infers that they must have been transported 
by the agency of ice. The probability of his conclusion is 
strengthened by the almost total absence of stratification in the 
deposit in question. 

* Brit Assoc., 1870, p. 8S. 



FORMER GLACIAL EPOCHS. 293 

North-west of Scotland. — Mr. J. Geikie tells me that much 
of the Cambrian conglomerate in the north-west of Scotland 
Btrongly reminds him of the coarse shingle beds (Alpine 
diluvium) which so often crowd the old glacial valleys of Swit- 
zerland and Northern Italy. In many places the stones of the 
Cambrian conglomerate have a subangular, blunted shape, like 
those of the r^-arranged moraine debris of Alpine countries. 

SILURIAN PERIOD. 

Wigtoumshire. — The possibility of glacial action so far back 
as the Silurian age has been suggested. In beds of slate and 
shales in Wigtownshire of Lower Silurian age Mr. J. Carrick 
Moore found beds of conglomerate of a remarkable character. 
The fragments generally vary from the size of one inch to a 
foot in diameter, but m some of the beds, boulders of 3, 4, and 
even 5 feet in diameter occur. There are no rocks in the 
neighbourhood from which any of these fragments could have 
been derived. The matrix of this conglomerate is sometimes 
a green trappean-looking sandstone of exceeding toughness, and 
sometimes an indurated sandstone indistinguishable from many 
common varieties of grey wacke.* 

Ayrshire. — Mr. James Geikie states that in Glenapp, and 
Dear Dalmellington, he foimd embedded in Lower Silurian 
fltrata blocks and boulders from one foot to 5 feet in diameter of 
gneiss, syenite, granite, &c., none of which belong to rocks of 
those neighbourhoods.t Similar cases have been found in Gal- 
way, Ireland, and at Lisbellaw, south of Enniskillen.J In 
America, Professor Dawson describes Silurian conglomerates 
with boulders 2 feet in diameter. 

Arctic Regions. — The existence of warm inter- glacial periods 
during that age may be inferred from the fact that in the 
arctic regions we find widespread masses of Silurian limestones 
containing cncrinites, corals, and mollusca, and other fossil 

• Quart. Joiim. Gool. Soc, vol. v., p. 10. Phil. Mag. for April, 1866, p. 289. 

t " Great Ice Age," p. 612. 

I Jukes' " ilanual of Geology," p. 421. 



294 CLIMATE AND TIME. 

remains, for an account of wluch see Professor Haugliton's 
geological account of the Arctic Archipelago appended to 
McGlintock's "Narrative of Arctic Discoveries," • 

OLD RED SANDSTONE. 

North of England. — ^According to Professor Ramsay and 
some other geologists the brecciated, subangular conglomerates 
and boulder beds of the Old Red Sandstone of Scotland and the 
North of England are of glacial origin. When these con- 
glomerates and the recent boulder clay come together it is 
difficult to draw the line of demarcation between them. 

Professor Ramsay observed some very remarkable facts in 
connection with the Old Red Sandstone conglomerates of Kirkby 
Lonsdale, and Sedburgh, in Westmoreland and Yorkshire. I 
shall give the results of his observations in his own words. 

" The result is, that we have found many stones and blocks 
distinctly scratched, and on others the ghosts of scratches nearly 
obliterated by age and chemical action, probably aided by 
pressure at a time when these rocks were buried under thou- 
sands of feet of carboniferous strata. In some cases, however, 
the markings were probably produced within the body of the 
rock itself by pressure, accompanied by disturbance of the 
strata ; but in others the longitudinal and cross striations con- 
vey the idea of glacial action. The shapes of the stones of 
these conglomerates, many of which are from 2 to 3 feet 
long, their flattened sides and subangular edges, together with 
the confused manner in which they are often arranged (like 
stones in the drift), have long been enough to convince me of 
their ice-borne character ; and the scratched specimens, when 
properly investigated, may possibly convince others, "t 

Isle of Man. — The conglomerate of the Old Red Sandstone in 
the Isle of Man has been compared by Mr. Gumming to " a 
consolidated ancient boulder clay." And he remarks, ** Was it 
80 that those strange trilobitic-looking fishes of that era had to 

• See alflo Quarterly Journal Geological Soc'etv, vol. xi., p. 610. 
t The Reader for August VI, 1866. 



FORMER GLACIAL EPOCHS. 295 

endure tlie buffeting of ice-waves, and to struggle amidst the 
wreck of ice-floes and the crush of bergs?"* 

Australia, — A conglomerate similar to that of Scotland has 
been found in Victoria, Australia, by Mr. Selwyn, at several 
localities. Along the Wild Duck Creek, near Heathcote, and 
also near the Mia-Mia, Spring Plains, Redesdale, localities in 
the Colony of Victoria, where it was examined by Messrs. 
Taylor and Etheridge, Junior, this conglomerate consists of a 
mixture of granite pebbles and boulders of various colours and 
textures, porphyries, indurated sandstone, quartz, and a pecu- 
liar flint-coloured rock in a matrix of bluish-grey very 
hard mud-cement, f Rocks similar to the pebbles and blo(ks 
composing the conglomerate do not occur in the immediate 
neighbourhood ; and from the curious mixture of large and 
small angular and waterwom fragments it was conjectured that 
it might possibly be of glacial origin. Scratched stones were 
not observed, although a careful examination was made. From 
similar mud-pebble beds on the Lerderderg River, Victcria, 
Mr. R. Daintree obtained a few pebbles grooved after the man- 
ner of ice-scratched blocks. :|^ 

And the existence of a warm condition of climate during the 
Old Red Sandstone period is evidenced by the fossiliferous lime- 
stones of England, Russia, and America. On the banks of the 
Athabasca River, Rupert-Land, Sir John Richardson found 
beds of limestone containing Productt\ Spiriferi, an Orthis re- 
sembling 0. rempinata, Terehratula reticularus,^ and a Pkuro* 
tomaria, which, in the opinion of the late Dr. Woodward, who 
examined the specimens, are characteristic of Devonian rocks 
of Devonshire. 

• " History of the IhIg of Man,*' p. 86. My colleague, Mr. John Home, in 
his "Sketch of the Geology of the Isle of Man," Trans, of Edin. Geol. Soc., 
Yol. ii., pait iii., considers this conglomerate to be of Lower Oarhoniferous age. 

t See Selwyn, " Phys. Geog^phy and Geology of Victoria.'* 1866. pp. Id- 
le ; Taylor and Kthoridge, Geol. ISwvey Vict., Quarter Sheet 13, N.E. 

iK<'port on the Geology oi the District of Ballan, Victoria. 1866. p, 11. 
Atrypa reticularis, 

14 



•^ CLIMATE AND TIME. 



CARBOXIFEROUS PERIOD. 

France. — It is now a good many years since Mr. Godinn* 
Austen directed attention to what he considered evidence of 
ice-action daring the coal period. This geologist found in the 
carboniferous strata of France large angular blocks which hr 
could not account for without inferring the former action of 
ice. '^ Wliether from local elevationy" he says, '' or from 
climatic conditions, there are certain appearances over the 
whole which imply that at one time the temperature must have 
been very low, as glacier-action can alone account for the 
presence of the large angular blocks which occur in the lowest 
detrital beds of many of the southern coal-basins.''* 

Scotland. — In Scotland great beds of conglomerate are mot 
with in various parts, which are now considered by Professor 
Goikie, Mr. James Geikic, and other officers of the Geological 
Survey who have had opportunities of examining them, to be 
of glacial origin. ** Tlioy are," says Mr. James Geikie, "quite 
unstratified, and the stones often show that peculiar blunts 
form which is so characteristic of glacial work." t ilany of the 
stones found by I^rofessor Geikie, several of which I have had 
an opportunity of seeing, arc well striated. 

In 1851 Professf^r Ilaughton brought forward at the Goo- 
logical Society of Dublin, a case of angular fragments of 
granite occurring in the carboniferous limestone of the county 
of Dublin ; and ho explained the phenomena by the supposition 
of the transporting p)wer of ice. 

North America, — In one of the North American coal-fields 
Professor Newl)erry found a boulder of quartzite 17 inches b\ 
VZ inches, imbedded in a seam of coal. Similar facts have 
also been recorded both in the United States, and in Nova 
Scotia. Professor Dawson describes what he calls a gigantic 
esker of Carboniferous age, on the outside of which large 

* Unart. Joum. Qeol. S')C.. vol. xii, p. 5S. 
t •* Gh«Ht Ice Age," p. 513. 



FORMER GLACIAL EPOCHS. 297 

travelled boulders were deposited, probably by drift-ice ; while 
in the swamps within, the coal flora flourished.* 

India, — Mr. W. T. Blanford, of the Geological Survey of 
iDdia, states that in beds considered to be of Carboniferous age 
are found large boulders, some of them as much as 15 feet in 
diameter. The bed in which these occur is a flue silt, and he 
refers the deposition of the boulders to ice- action. Within the 
last three years his views have received singular confirmation 
in another part of India, where beds of limestone were found 
striated below certain overlying strata. The probability that 
these appearances are due, as Mr. Blanford says, to the action 
of ice, is strengthened by the consideration that about five 
degrees farther to the north of the district in question rises 
the cold and high table-land of Thibet, which during a glacial 
epoch would undoubtedly be covered with ice that might well 
descend over the plains of India.t 

Arctic Regions, — ^A glacial epoch during the Carboniferous 
age may be indirectly inferred from the probable existence of 
warm inter-glacial periods, as indicated by the limestones with 
fossil remains found in arctic regions. 

That an equable condition of climate extended to near the 
north pole is proved by the fact that in the arctic regions vast 
masses of carboniferous limestone, having all the characters of 
the mountain limestone of England, have been found. *' These 
limestones," says Mr. Isbister, " are most extensively deve- 
loped in the north-east extremity of the continent, where they 
occupy the greater part of the coast-line, from the north side 
of the Kotzebue Sound to within a few miles of Point Barrow, 
and form the chief constituent of the lofty and conspicuous 
headlands of Cape Thomson, Cape Lisbum, and Cape Sabine." J 
Limestone of the same age occurs extensively along the Mac- 
kenzie River. The following fossils have been found in these 
limestones : — Terebrafuia resupinata,^ Lithostrotion hamlti/orme^ 
Ct/athophyllum dianthitm^ C, flexuosum, Turbinolia miiraia, Pro* 

• •♦ Great Ice Age," p. /513. f Brit. Assoc. Report for 1873. 

X Quart. Joura. Gool. Soc, vol. xi., p. 619. § OrthU ruupiruUa, 



X98 CLIMATE AND TIME. 

ductus Martini,* Dentaiiutn Sarcinuh, Spiriferi, Orthidre, and 
encrinital fragments in the greatest abundance. 

Among the fossils brought home from Depot Point, Albert 
Land, by Sir E. Belcher, Mr. Salter found the following, 
belonging to the Carboniferous period: — FusuUna hi/perborea, 
Stylastrea inconferta, Zaphrentis ociboa, ClisiophyUum tumulus, 
Syringopora (Aulopora), Fenestelia Arctica^ Spirifera Keiihavit, 
Productus cora, P. semireticulatus.f 

Coal-beds of Carboniferous age are extensively developed in 
arctic regions. The fuel is of a highly bituminous character, 
resembling, says Professor Haughton, the gas coals of Scotland. 
The occurrence of coal in such high latitudes indicates beyond 
doubt that a mild and temperate condition of climate must, 
during some part of the Carboniferous age, have prevailed up 
to the very pole. 

'* In the coal of Jameson's Land, on the cast side of Green* 
land, lying in latitude 71^, and in that of Melville Island, in 
latitude 75° N., Professor Jameson found plants resembling 
fossils of the coal-fields of Britain."? 

TERMIAN PERIOD 

England, — From the researches of Professor Ramsay in the 
Permian breccias, wo have every reason to believe that during 
a part of the Permian ago our country was probably covered 
with glaciers reaching to the sea. These brecciated stones, he 
states, are mostly angular or subangular, with flattened sides 
and but very slightly rounded at the edges, and are imbedded 
in a deep red marly paste. At Abberley Hill some of the 
masses are from 2 to 3 feet in diameter, and in one of the 
quarries, near the base of Woodbury Hill, Professor Ramsay 
saw one 2 feet in diameter. Another was observed at Wood- 
bury Rock, 4 feet long, 3 feet broad, and IJ feet thick. 
The boulders were found in South Stafford&luro, Enville, in 

• IVod, nemircticulatu* var. Martini, Sow. 

t « Belcher's Voyu^re," vol. ii., p. 377. 

j "Joumtd of a ho.it Voyage through Rupert-Liind," vol. ii., p. 208- 



FORMER GLACIAL EPOCHS. S99 

Abberley and Malvern Hills, and other places. " They eeem," 
he says, "to have been derived from the conglomerate and 
green, grey, and purple Cambrian grits of the Longmynd, and 
from the Silurian quartz-rocks, slates, felstones, felspathio 
ashes, greenstones, and Upper Caradoc rocks of the country 
between the Longmynd and Chirbury. But then," he con- 
tinues, " the south end of the Malvern Hills is from forty to 
fifty miles, the Abberleys from twenty-five to thirty-five miles, 
Enville from twenty to thirty miles, and South Staflbrdshire 
from thirty -five to forty miles distant from that country."* 

It is physically impossible. Professor Ramsay remarks, 
that these blocks could have been transported to such distances 
by any other agency than that of ice. Had they been trans- 
ported by water, supposing such a thing possible, they would 
have been rounded and water-worn, whereas many of these 
stones are flat slabs, and most of them have their edges but 
little rounded. And besides many of them are highly polished, 
and others grooved and finely striated, exactly like those of 
the ancient glaciers of Scotland and Wales. Some of these 
specimens are to be seen in the Museum of Practical Geology, 
Jermyn Street. 

Scotland. — In the Island of Arran, Mr. E. A. Wunsch and 
Mr. James Thomson found a bed of conglomerate which they 
considered of Permian age, and probably of glacial origin. 
This conglomerate enclosed angular fragments of various 
schistose, volcanic, and limestone rocks, and contained carboni- 
ferous fossils. 

IrciamL — At Armagh, Ireland, Professor Hull found boulder 
beds of Permian age, containing pebbles and boulders, some- 
tivnes 2 feet in diameter. Some of the boulders must have 
been transported from a region lying about 30 miles to the north- 
west of the locality in which they now occur. It is difficult 
to conceive, says Professor Hull, how rock fragments of such 
a size could have been carried to their present position by any 
other agency than that of floating ice. This boxdder-bed is 

* Quart Joum. Geol. Soc., vol. zi., p. 197 



|oo CLIMATE AND TIME. 

overlaid by a recent bed of boulder clay. Professor Ramsay^ 
wbo also examined the section, agrees with Professor Hull thai 
the bed is of Permian age, and unquestionably of ice-forma- 
tion.* 

Professor Ramsay feels convinced that the same conclusions 
which he has drawn in regard to the Permian breccia of 
£ngland will probably yet be found to hold good in regard 
to much of that of North Germany, t And there appears to 
be some ground for concluding that the cold of that period 
even reached to India.^ 

South Africa, — An ancient boulder clay, supposed to be either 
of Permian or Jurassic age, has been extensively found in 
Natal, South Africa. This deposit, discovered by Dr. Suther- 
land, the Surveyor-General of the colony, is thus described by 
Dr. Mann : — 

"The deposit itself consists of a greyish-blue argillaceous 
matrix, containing fragments of granite, gneiss, graphite, 
quartzite, greenstone, and clay-slate. These imbedded frag- 
ments are of various size, from the minute dimensions of 
sand-grains up to vast blocks measuring 6 feet across, and 
weighing from 5 to 10 tons. They are smoothed, as if they 
had been subject to a certain amount of attrition in a muddy 
sediment ; but they are not roimded like boulders that have 
been subjected to sea-breakers. The fracture of the rock is 
not conchoidal, and there is manifest, in its substance, a rude 
disposition towards wavy stratification." 

" Dr. Sutherland inclines to think that the transport of vast 
massive blocks of several tons' weight, the scoring of the sub- 
jacent surfaces of sandstone, and the simultaneous deposition 
of minute sand-grains and large boulders in the same matrix, 
all point to one agency as the only one which can be rationally 
admitted to account satisfactorily for the presence of this 
remarkable formation in the situations in which it is found. 
He believes that the boulder-bearing clay of Natal is of 

• Pixplanation Memoir to Sheet 47, " Geological Survey of Ireland.** 

t Phil. Mag., vol. xxix., p. 290. 

J •* Meinoira of the Geological Survey of India/* vol. i., part L 



FORMER GLACIAL EPOCHS. 30J 

analogous nature to the great Scandinayian driffcy to wMcli it is 
certainly intimately allied in intrinsic mineralogical character ; 
that it is virtually a vast moraine of olden time ; and that ice, 
in some form or other, has had to do with its formation, at least 
so far as the deposition of the imbedded fragments in the 
amorphous matrix are concerned." * 

In the discussion which followed the reading of Dr. Suther- 
land's paper, Professor Ramsay pointed out that in the Natal 
beds enormous blocks of rock occurred, which were 60 or 80 
miles from their original home, and still remained angular; 
and there was a difficulty in accounting for the phenomena on 
any other hypothesis than that suggested. 

Mr. Stow, in his paper on the Karoo beds, has expressed a 
similar opinion regarding the glacial character of the forma- 
tion, t 

But we have in the Karoo beds evidence not only of glacia- 
tion, but of a much warmer condition of things than presently 
exists in that latitude. This is shown from the fact that the 
shells of the TV^omi-beds indicate a tropical or subtropical 
condition of climate. 

Arctic Regions. — ^The evidence which we have of the exist- 
ence of a warm climate during the Permian period is equally 
conclusive. The close resemblance of the flora of the Permian 
period to that of Carboniferous times evidently points to the 
former prevalence of a warm and equable climate. And the 
existence of the magnesian limestone in high latitudes seems 
to indicate that during at least a part of the Permian period, 
just as during the accumulution of the carboniferous lime- 
stone, a warm sea must have obtained in those latitudes. 

OOLITIC PERIOD. 

North of Scotland, — There is not wanting evidence of some- 
thing like the action of ice during the Oolitic period. J 

In the North of Scotland Mr. James Geikie says there is a 

* Quart. Jouni. Geol. 800., vol. xxvi., p. 614. 

t Ibid., vol. xxvii.y p. 644. 

I Phil. Mag., vol. xxix., p. 290. 



|oi CLIMATE AND TIME. 

coarse boulder conglomerate associated with the Jurassic strata 
in the east of Sutherland, the possibly glacial origin of which 
long ago suggested itself to Professor Eramsay and other ob- 
servers. Mr. Judd believes the boulders to have been floated 
down by ice from the Highland mountains at the time the 
Jurassic strata were being accumulated. 

North Oreenland, — During the Oolitic period a warm condi- 
tion of climate extended to North Greenland. For example, in 
Prince Patrick's Island, at Wilkie Point, in lat. 76° 20' N., 
and long. 117° 20' W., Oolitic rocks containing an ammonite 
{Ammonites McClintockiy Haughton), like A, concavm and other 
shells of Oolitic species, were found by Captain McClintock,* 
In Katmai Bay, near Behring's Straits, the following Oolitic 
fossils were discovered — Ammonites Wa^nessenskii, A, hiplex^ 
Belemnites paxlllosus, and Unio liasainus.f Captain McClintock 
found at Point Wilkie, in Prince Patrick's Island, lab. 76° 20', 
a bone of lehthyosaurus, and Sir E. Belcher found in Exmouth 
Island, lat. 76° 16' N., and long. 96° W., at an elevation of 
670 feet above the level of the sea, bones which were examined 
by Professor Owen, and pronounced to be those of the same 
animal. J Mr. Salter remarks that at the time that these 
fossils were deposited, " a condition of climate something like 
that of our own shores was prevailing in latitudes not far short 
of 80° N."§ And Mr. Jukes says that during the Oolitic 
period, " in latitudes where now sea and land are bound in ice 
and snow throughout the year, there formerly flouri.>hed animals 
and plants similar to those living in our own province at that 
time. The questions thus raised," continues Mr. Jukes, " as to 
the climate of the globe when cephalopods and reptiles such as 
we should expect to find only in warm or temperate seas, could 
live in such high latitudes, are not easy to answer.'MI And 

» Journal of the Royal Dublin Society for February, 18o7. 
t Qtmrfc. Jourii. Go<>l. Soc , vol. xi., p. 619. 

X **Tho Lost of the Arctic Voyages/* by Captjiin Sir E. Belcher, vol. ii., \». 
389. Appendix Brit. Assoc. Report lor 1855, p. 79 
6 Ibid., vol. ii., p. 379. Appendix, 
i '* Manual of Geology/' pp. 395, 493. 



FORMER GLACIAL EPOCHS. 303 

Professor Haughton remarks, that he thinks it highly impro- 
bable that any change in the position of land and water could 
ever have produced a temperature in the sea at 76° north lati- 
tude which would allow of the existence of ammonites, espe- 
cially species so Kke those that lived at the same time in 
the tropical warm seas of the South of England and France at 
the close of the Liassic, and commencement of the Lower Oolitic 
period.* 

The great abundance of the limestone and coal of the Oolitic 
system shows also the warm and equable condition of the 
climate which must have then prevailed. 

CRETACEOUS PERIOD. 

Croydon. — A large block of crj'^stalline rock resembling 
granite was found imbedded in a pit, on the side of the old 
London and Brighton road near Purley, about two miles south 
of Croydon. Mr. Godwin-Austen has shown conclusively that 
it must have been transported there by means of floating ice. 
This boulder was associated with loose sea-sand, coarse shingle, 
and a smaller boulder weighing twenty or twenty-five pounds, 
and all water- worn. These had all sunk together without 
separating. Hence they must have been firmly held together, 
both during the time that they were being fioated away, and also 
whilst sinking to the bottom of the cretaceous sea. Mr. Godwin- 
Austen supposes the whole to have been carried away frozen to 
the bottom of a mass of ground-ice. When the ice from melting 
became unable to float the mass attached to it, the whole would 
then sink to the bottom together. t 

Dover, — While the workmen were employed in cutting the 
timnel on the London, Chatham, nnd Dover Railway, between 
Lydden Hill and Shepherdswell, a few miles from Dover, they 
came upcm a muss of coal imbedded in chalk, at a depth of 180 
feet. It was abi)ut 4 feet square, and from 4 to 10 inches thick. 

♦ App»'ndix to McClintook's ** Arctic DiBCoveries.** 

t Quart. Journ. Geol. Soc, vol. xiv., p. 262. Brit. Assoc. Report for 18o7i 
p. 02. 



304 CLIMATE AND TIME. 

The coal was friable and highly bituminous. It resembled some of 
the Wealden or Jurassic coal, and was unlike the true coal of 
the coal-measures. The specific gravity of the coal precluded 
the supposition that it could have floated away of itself into the 
cretaceous sea. " Considering its friability," says Mr. Godwin- 
Austen, '' I do not think that the agency of a floating tree 
could have been engaged in its transport ; but, looking at its 
flat, angular form, it seems to me that its history may agree 
with what I have already suggested with reference to the 
boulder in the chalk at Croydon. We may suppose that during 
the Cretaceous period some bituminous beds of the preceding 
Oolitic period lay so as to be covered with water near the sea- 
margin, or along some river-bank, and from which portions 
could be carried off by ice, and so drifted away, until the ice 
was no longer able to support its load.*** 

Mr. Godwin- Austen then mentions a number of other cases 
of blocks being found in the chalk. In regard to those cases 
he appropriately remarks that, as the cases where the occurrence 
of such blocks has been observed are likely to be far less 
numerous than those which have escaped observation, or failed 
to have been recorded, and as the chalk exposed in pits and 
quarries bears only a most trifling proportion to the whole 
horizontal extent of the formation, we have no grounds to con- 
clude that the above are exceptional cases. 

Boulders have also been found in the crelaceous strata of 
the Alps by Escher*von der Linth.f 

The existence of warm periods during the Cretaceous age is 
plainly shown by the character of the flora and fauna of that 
age. The fact that chalk is of organic origin implies that the 
climate must have been warm and genial, and otherwise favour- 
able to animal life. This fe further manifested by such plants 
as Cycm and ZamiUy which betoken a warm climate, and by 
the corals and huge sauroid reptQes which then inhabited our 
waters. 

* QuHrt. Joiim. Geol. Soc, toI. xvi., p. 327* Geologisty I860, p. 3S. 
t Phil. Mug., vol. xxix., p. 290. 



FORMER GLACIAL EPOCHS. 305 

It is, in fact, the tropical character of the &una of that 
period which induced Sir Charles Lyell to reject Mr. Godwin- 
Austen's idea that the boulders found in the chalk had been 
transported by floating ice. Such a supposition, implying a 
cold climate, **i8," Sir Charles says, "inconsistent with the 
luxuriant growth of large chambered univalves, numerous 
corals, and many fish, and other fossils of tropical forms." 

The recent discovery of the Cretaceous formation in Green- 
land shows that during that period a mild and temperate 
condition of climate must have prevailed in that continent up 
to high latitudes. ** This formation in Greenland," says 
Dr. Robert Brown, "has only been recently separated from 
the Miocene formation, with which it is associated and was 
supposed to be a part of. It is, as far as we yet know, only 
found in the vicinity of Eome or Eoke, near the shores of 
Omenak Fjord, in about 70° north latitude, though traces 
have been found elsewhere on Disco, &c. The fossils hitherto 
brought to Europe have been very few, and consist of plants 
which are now preserved in the Stockholm and Copenhagen 
Museums. From these there seems little doubt that the age 
assigned to this limited deposit (so far as we yet know) by the 
celebrated palaeontologist, Professor Oswald Heer, of Zurich, 
is the correct one."* Dr. Brown gives a list of the Cretaceous 
flora found in Greenland. 

EOCENE PERIOD. 

Sicitzerland. — In a coarse conglomerate belonging to the 
*^ flysch " of Switzerland, an Eocene formation, there are found 
certain immense blocks, some of which consist of a variety of 
granite which is not known to occur in situ in any part of the 
Alps. Some of the blocks are 10 feet and upwards in length, 
and one at Haiekeren, at the Lake of Thun, is 105 feet in 
length, 90 feet in breadth, and 45 feet in height. Similar 
blocks are found in the Apennines. These unmist/akably 

* Trans. OeoL Soc. of Glasgow, ▼ol. t., p. 64. 



|o6 CLIMATE AND TIME. 

indicate tho presence of glaciers or floating ice. This conclu« 
sion is further borne out by the fact that the ^^flysch " is desti- 
tute of organic remains. But the hypothesis that these huge 
masses were transported to their present sites by glaciers or 
floating ice has been always objected to, says Sir Charles 
Lyelly '' on the ground that the Eocene strata of Nummulitio 
age in Switzerland, as well as in other parts of Europe, contain 
genera of fossil plants and animals characteristic of a warm 
climate. And it has been particularly remarked," he continues, 
'' by M. Desor that the strata most nearly associated with the 
*fly8ch ' in the Alps are rich in echinoderms of the Spatangtis 
family which have a decided tropical aspect."* 

But according to the theory of Secular Changes of Climate, 
the very fact that the ^^flf/sch " is immediately associated with 
beds indicating a warm or even tropical condition of climate, is 
one of the strongest proofs which could bo adduced in favour of 
its glacial character, for the more severe a cold period of a 
glacial epoch is, the warmer will be the j)eriod8 which inune- 
diately precede and succeed. These crocodiles, tortoises, and 
tropical flora probably belong to a warm Eocene inter-glacial 
period. 

MIOCENE PERIOD. 

Italy. — ^We have strong evidence in favour of the opinion 
that a glacial epoch existed during the Miocene period. It has 
been shown by M. Gastiildi, that during that ago Alpine 
glaciers extended to tho sea-level. 

Near Turin there is a series of hills, rising? about 500 or GOO 
feet above the valleys, composed of beds of Miocene sandstone, 
marl, and gravel, and loose conglomerate. These beds have 
been carefully examined and described by M. Gastiildi. t The 
hill of the Luperga has been particularly noticed by him. 
Many of the stones in these beds are striated in a manner 
similar to those found in the true till or boulder clay of this 

• "Principles," vol. i., p. 209. Eleventh Edition. 

t ** Memoirs of the Koyal Academy of Science of Turin/* S«cond 8f*rie«, 
vol. XX. I am indebted for the above pailiculais to Professor Itam-ay, wh« 
risited the spot along with M. Gastaldi. 



FORMER GLACIAL EPOCHS. 307 

country. Eut what is most remarkable is the fact that large 
erratic blocks of limestone, many of them from 10 to 16 feet in 
diameter, are found in abundance in these beds. It has been 
shown by Qastaldi that these blocks have all been derived from 
the outer ridge of the Alps on the Italian side, namely, from 
the range extending from Ivrea to the Lago Maggiore, and con- 
sequently they must have travelled from twenty to eighty miles. 
So abundant are these large blocks, that extensive quarries have 
been opened in the hills for the sake of procuring them. These 
facts prove not only the existence of glaciers on the Alps during 
the Miocene period, but of glaciers extending to the sea and 
breaking up into icebergs; the stratification of the beds 
amongst which the blocks occur sufficiently indicating aqueous 
action and the former presence of the sea. 

That the glaciers of the Southern Alps actually reached to 
the sea, and sent their icebergs adrift over what are now the 
sunny plains of Northern Italy, is sufficient proof that during 
the cold period of Miocene times the climate must have been 
very severe. Indeed, it may well have be^n as severe as, if 
not even more excessive than, the intensest severity of climate 
experienced during the last great glacial epoch. 

Greenland. — Of the existence of warm conditions during 
Miocene times, geology afibrds us abundant evidence. I shall 
quote the opinion of Sir Charles Lyell on this point : — 

** We know," says Sir Charles, " that Greenland was not 
always covered with' snow and ice ; for when we examine the 
tertiary strata of Disco Island (of the Upper Miocene period), 
we discover there a multitude of fossil plants which demonstrate 
that, like many other parts of the arctic regions, it formerly 
enjoyed a mild and genial climate. Among the fossils brought 
from that island, lut. 70° N., Professor Hecr has recognised 
Sequoia Landsdorfii, a coniferous species which flourished 
throughout a great part of Europe in the Miocene period. The 
same plant has been foimd fossil by Sir John Richardson within 
the Arctic Circle, far to the west on the Mackenzie River, near 
the entrance of Bear River ; also by some Danish naturalists in 



308 CLIMATE AND TIME. 

Iceland, to the east. The Icelandic snrturband or lignite, of 
this age, has also yielded a rich harvest of plants, more than 
thirty-one of them, according to Steenstrup and Heer, in a 
good state of preservation, and no less than fifteen specifically 
identical with Miocene plants of Europe. Thirteen of the 
number are arborescent; and amongst others is a tulip-tree 
(Liriodendron), with its fruit and characteristic leaves, a plane 
{Platanm), a walnut, and a vine, affording unmistakable 
evidence of a climate in the parallel of the Arctic Circle which 
precludes the supposition of glaciers then existing in the neigh- 
bourhood, still less any general crust of continental ice like 
that of Greenland." * 

At a meeting of the British Association, held at Nottingham 
in August 1866, Professor Heer read a valuable paper on the 
"Miocene Flora of North Greenland." In this paper some 
remarkable conclusions as to the probable temperature of 
GJreenland during the Miocene period were given. 

Upwards of sixty different species brought from Atane- 
kerdluk, a place cgi the Waigat opposite Disco, in lat. 7QP N., 
have been examined by him. 

A steep hill rises on the coast to a height of 1,080 feet, and 
at this level the fossil plants are found. Large quantities of 
wood in a fossilized or carbonized condition lie about. Captain 
Inglefield observed one trunk thicker than a man's body stand- 
ing upright. The leaves, however, are the most important 
portion of the deposit. The rock in which they are found is a 
sparry iron ore, which turns reddish brown on exposure to the 
weather. In this rock the leaves are found, in places packed 
closely together, and many of them are in a very perfect con- 
dition. They give us a most valuable insight into the nature 
of the vegetation which formed this primeval forest. 

He arrives at the following conclusions : — 

1. The fossilized plants of Atanekerdluk cannot have been dri/tea 
from any great distance. They must have grown on the spot tc/^re 
ihey were found, 

• " Anliqnity of Man," Second Edition, p. 237 



FORMER GLACIAL EPOCHS. jog 

This is shown — 

(a) By the fact that Captain Inglefield and Dr. Buik 
observed trunks of trees standing upright. 

(&) By the great abundance of the leaves, and the perfect 
state of preservation in which they are found. 

(c) By the fact that we find in the stone both fruits and 
seeds of the trees whose leaves are also found there. 

{d) By the occurrence of insect remains along with the 
leaves. 

2. The flora of Atanekerdluk is Miocene, 

3. The flora is rich in species, 

4. The flora proves without a doubt that North Oreenland^ in 
the Miocene epochs had a climate much warmer than its present one. 
The difference must he at least 29° F. 

Professor Heer discusses at considerable length this proposi- 
tion. Ho says that the evidence from Greenland gives a final 
answer to those who objected to the conclusions as to the 
Miocene climate of Europe drawn by him on a former occasion. 
It is quite impossible that the trees found at Atanekerdluk 
could ever have flourished there if the temperature were not far 
higher than it is at present. This is clear from many of the 
species, of which we find the nearest living representative 10*^ 
or even 20° of latitude to the south of the locality in question. 

The trees of Atanekerdluk were not, he says, all at the 
extreme northern limit of their range, for in the Miocene flora 
of Spitzbergen, lat. 78° N., we find the beech, plane, hazelnut, 
and some other species identical with those from Greenland, 
and we may conclude, he thinks, that the firs and poplars which 
we meet at Atanekerdluk and Bell Sound, Spitzbergen, must 
have reached up to the North Pole if land existed there in the 
tertiary period. 

" The hilla of fossilized wood," he adds, *' found by McClure 
and his companions in Banks's Land (lat. 74° 27' N.), are there- 
fore discoveries which should not astonish us, they only confirm 
the evidence as to the original vegetation of the polar regions 
which we have derived from other sources." 



Sio CLIMATE AND TIME. 

The Sequoia Landadorfii is the most abundant of the trees of 
Atanekerdluk. The Sequoia sempairvcus is its present repre- 
sentative. This tree has its extreme northern limit about lat. 
53^ N. For its existence it requires a summer temperature of 
59° or 61° F. Its firuit requires a temperature of 64° for 
ripening. The winter temperature must not fall below 34°, 
and that of the whole year must be at least 49°. The tempera- 
ture of Atanekerdluk during the time that the Miocene flora 
grow could not have been under the above.* 
Professor Heer concludes his paper as follows : — 
" I think these facts are convincing, and the more so that 
they are not insulated, but confirmed by the evidence derivable 
from the Miocene flora of Iceland, Spitzbergen, and Northern 
Canada. These conclusions, too, are only links in the grand 
ehain of evidence obtained from the examination of the Miocene 
flora of the whole of Europe. They prove to us that we could 
not by any rc-arrangement of the relative positions of land and 
water produce for the northern hemisphere a climate which 
would explain the phenomena in a satisfactory manner. We 
must only admit that we are face to face with a problem, whose 
solution in all probability must be attempted, and, we doubt not, 
completed by the astronomer." 

• Dr. Hobert Brown, in a recent Memoir on the l^Iiocene Beds of the Disro 
District (TranH. Gool. 8oc. Glaspr., vol. v., p. 65), has added considerably to our 
knowledge of these deposits. He describes the strata in detail, and gives lists ot 
the plant and animal remains discovered by himself and othern, and described by 
Professor Heer. Professor KordonHkjbId has likewise increased the data at our 
command (Transaiitions of the Swedish Academy, 1873) ; and still furth(^r 
evidence in favour of a warm climate having prevailed in Greenland during 
Miocene times has been obtained by the recent second German polar expedition. 



CHAPTER XIX. 

aaOLOOICAL time. — FJIOBABLE date of the GIACIAL SPOCH. 

Geological Time measunible from Aiitronomical Data. — 'M. Leverrier's FormulsBi 
—Tables of Eccentricity for 3,000,000 Years in the Past and l,OOu,O00 
Years in the Future. — Uow the Tables have been computed. — Why the 
Qlacial Epoch is more recent thHn had been supposed. — Figures convey a 
very inadequate Concepti(m of immense Dumtion. — Mode of representing a 
Aliliion of Years. — rrobable Dale of the Glacial Epoch. 

If those great Secular variations of climate which we have been 
consideriug be indirectly the result of changes in the eccen- 
tricity of the earth's orbit, then we have a means of deter- 
mining, at least so far as regards recent epochs, when these 
variations took place. If the glacial epoch be due to the 
causes assigned, we have a means of ascertaining, with tolerable 
accuracy, not merely the date of its commencement, but the 
length of its duration. M. Leverrier has not only determined 
the superior limit of the eccentricity of the earth's orbit, but 
has also given formulae by means of which the extent of the 
eccentricity for any period, past or future, may be computed. 

A well-known astronomer and mathematician, who has 
specially investigated the subject, is of opinion that these 
formulae give results which may be depended upon as approxi- 
mately correct for four millions of years past and future. An 
eminent physicist has, however, expressed to me his doubts 
as to whether the results can be depended on for a period so 
enormous. M. Leverrier in his Memoir has given a table of 
the eccentricity for 100,000 years before and after 1800 a.d., 
computed for intervals of 10,000 years. This table, no doubt, 
embraces a period sufficiently great for ordinary astronomical 
purposes, but it is by far too limited to afford information in 
regard to geological epochs. 



312 ' CLIMATE AND TIME. 

With tlie view of ascertaining the probable date of the 
glacial epoch, as well as the character of the climate for a long 
course of ages, Table I. was computed from M. Leverrier's 
formulae.* It shows the eccentricity of the earth's orbit and 
longitude of the perihelion for 3,000,000 of years back, and 
1,000,000 of years to come, at periods 50,000 years apart. 

On looking over the table it will be seen that there are 
three principal periods when the eccentricity rose to a very high 
value, with a few subordinate maxima between. It will be 
perceived also that during each of those periods the eccentricity 
does not remain at the same uniform value, but rises and falls, 
in one case twice, and in the other two cases three times. 
About 2,650,000 years back we have the eccentricity almost at 
its inferior limit. It then begins to increase, and fifty thousand 
years afterwards, namely at 2,600,000 years ago, it reaches 
0660 ; fifty thousand years after this period it has diminished 
to "0167, which is about its present value. It then begins to 
increase, and in another fifty thousand years, namely at 
2,500,000 years ago, it approaches to almost the superior limit, 
its value being then '0721. It then begins to diminish, and at 
2,450,000 years ago it has diminished to -0252. These two 
maxima, separated by a minimum and extending over a period 

• The following are W. T/everrier*8 formulae for computing the eccentricity 
of the earth's orbit, given in his "Memoir" in the Coitnaiseance drs Temps ioi 
1848:— 

Eccentricity in {t) years after January 1, 1800 = ^h'^ -\- b where 
k = 0-000526 Sin (^^-fi3)-f 0-0166 11 Sin (^/ + W + 0002366 Sin (^,^ + ^i) 

4-0010622 SinM-|-/^») —0018926 Sin &/4 A) 
4-0-011782Sin(i'6^-f/35)— 0-016913 Sin (^e'-hft) 
uid 

/ = 0-000626 Cos {gt^P)J^ 0-016611 Cos (^/-f /3,) +00023CS Cos (j^/ + /3,) 

-f 0010622 Cos {g^t -f ^,) — 0.018925 Cos {g^t -j- ft) 
4- 0011782 Cos Q^i H- ft) — 0016913 Cos (get + ft) 

g = 2''-2o842 
^, = 3''-71364 
g^ as 22*-4273 
y,=: 6''-2989 
g,^ r'57i7 
g, = 17''1627 
g% = l7'-8633 



/8 = 


126^ 


43' 


15" 


ft = 


27 


21 


26 


/3.= 


126 


44 


8 


^3 = 


85 


47 


45 


/3, = 


35 


38 


43 


1^5 = 


— 25 


11 


33 


^ = 


— 45 


28 


69 



J L x^ •> 




■f, .. I 



i I f I I 



_-i 



GEOLOGICAL TIME. 313 

of 200,000 years, constitute the first great period of high 
eccentricity. We then pass onwards for upwards of a mQlion 
and a half years, and we come to the second great period. 
It consists of three maxima separated by two minima. The 
first maximum occurred at 950,000 years ago, the second 
or middle one at 850,000 years ago, and the third and last at 
750,000 years ago — the whole extending over a period of nearly 
300,000 years. Passing onwards for another million and half 
years, or to about 800,000 years in the future, we come to the 
third great period. It also consists of three maxima one hua« 
dred thousand years apart. These occur at the periods 800,000, 
900,000, and 1,000,000 years to come, respectively, separated 
also by two minima. Those three great periods, two of them 
in the past and one of them in the future, included in the Table, 
are therefore separated from each other by an interval of 
upwards of 1,700,000 years. 

In this Table there are seven periods when the earth's orbit 
becomes nearly circular, four in the past and three in the future. 

The Table shows also four or five subordinate periods of high 
eccentricity, the principal one occurring 200,000 years ago. 

The variations of eccentricity during the four millions of 
years, are represented to the eye diagrammitically in Plate IV. 

In order to determine with more accuracy the condition of 
the earth's orbit during the three periods of great eccentricity 
included in Table I., I computed the values for periods of ten 
thousand years apart, and the results are embodied in Tables 
II., III., and IV. 

There are still eminent astronomers and physicists who* are 
of opinion that the climate of the globe never could have been 
seriously afiected by changes in the eccentricity of its orbit. 
This opinion results, no doubt, from viewing the question as a 
purely astronomical one. Viewed from an astronomical stand- 
point, as has been already remarked, there is actually nothing 
from which any one could reasonably conclude with certainty 
whether a change of eccentricity would seriously affect climate 
or not. By means of astronomy we ascertain the extent of the 



CLIMATE AND TIME. 



Tub Ecckhtbicttt and Lomoitudb at ' 
8,000,000 YsAita is tub Past ami 
i^tu Lntkbial8 of 60,(11)0 YBjUU. 



I Fbbihelion at tub Eabth'* Obbit i 
,000,DDO Ybabi im thb Futvm, comvoi 



FAST TIMK. 


lAST TISIE. 


NnmlBTofiHir. 
Tiefare epoch J(Wl. 

— 3,000,000 




^3?"*' 


bcA.ie epoch JSUO. 


EcetDlricity 


lasr 


00305 


39 30 


— 1,950,000 


00427 


120 32 


— 2,050,000 


0-0170 


210 39 


— 1,900,000 


0-033G 


188 31 


— 2,900,000 


0-0442 


200 52 


— 1,850,000 


0-0503 


272 14 


— 2,850,000 


0-0416 


18 


— 1,800,000 


0-0334 


354 52 


— 2.800,000 


0-0,3.52 


339 14 


— 1,750,000 


00350 


65 25 


— 2,750,000 


0320 


101 22 


— 1,700,000 


0-0085 


95 13 


— 2,700,000 


0-0330 


65 37 


— 1,050,000 


00035 


168 23 


— 2,650,000 


0-0053 


318 40 


— 1,600,000 


0-0305 


158 42 


~ 2,000,000 


0-OG60 


190 4 


- 1,550,000 


0-0239 


225 57 


— 2,550,000 


0-0107 


298 34 


— 1,-500,000 


0-0430 


303 29 


— 2,500,000 


0-0721 


338 36 


— 1.450,000 


0-0195 


57 11 


— 3,450,000 


0-02-52 


109 33 


— 1.400.000 


0-0315 


97 35 


— 2,400,000 


0-0415 


116 40 


- 1.350.000 


0032'J 


293 38 


— 2,350,000 


0-0281 


308 23 


— 1.300.000 


0-0022 


48 


— 2,300,000 


00238 


195 25 


— 1.250,000 


0-0475 


105 50 


— 2,250,000 


0-0328 


141 18 


— 1.200,000 


0-0289 


239 34 


— 2,200,000 


0-0352 


307 6 


- 1,150,000 


00473 


250 27 


— 2,150,000 


0-0183 


307 5 


— 1,100,000 


0-0311 


55 24 


— 2,100,000 


0-0304 


98 40 


— 1,0-50,000 


00-326 


4 8 


— 2,050.000 


0-0170 


334 46 








— 2,000,000 


0-0138 


324 4 









GEOLOGICAL TIMS. 



TABLE l.—Continatd. 



ru 




D Losonc 


!>■ or tnB 


PmtliUOH OF THl Earth- 


Ohbit fob 




3,OOU,0Ua YUBII IK THB 1 


AHT AXD 1,000,000 YUSS IM 


lua Fi-Tuj, 


B, OOMPDna 




?aB iNTEBUU «F ^0,000 YttlU. 












PAW Tl«& 


JtJTDBE TIAIB. 




£^'iSK 


£o»Dtrldtr 


1.(nieitndB of 
penlH.Li«i. 


Numlwrof VHiA 
•Aor opocli lnw. 




ISffi.- 




—1,000,000 


00101 


218 22 


A.D 


1800 


0-01C8 


99 30 




— 950,000 


00517 


97 01 


+ 


60.000 


0-0173 


38 12 




_ 900,000 


0-0102 


135 2 


+ 


100,000 


0-0191 


114 50 




— 800,000 


0-0747 


230 28 


+ 


150,000 


0-0303 


201 57 




— 800,000 


00I:13 


343 49 


+ 


200.000 


0-0246 


279 41 




_ 700,000 


00070 


27 18 


-t- 


250.000 


0-0286 


350 54 




_ 700,000 


0-0220 


208 13 


+ 


300,000 


0-0158 


172 29 




— 600.000 


0-0220 


141 29 


+ 


350,000 


0-0098 


201 40 




— COO.OOO 


0-0417 


32 34 


+ 


400,000 


0-0429 


6 9 




— 000,000 


0-0100 


201 50 


+ 


450,000 


0-0231 


98 37 




— 000.000 


0-0388 


193 06 


+ 


500,000 


0-0534 


157 26 




_ 400,000 


0-0308 


356 52 


-f 


500,000 


0-0259 


287 31 




_ 400,000 


0-0170 


290 7 


+ 


600,000 


0-0395 


285 43 




- 300,000 


0-0105 


182 SO 


+ 


650,000 


0-0169 


144 3 




— 300.000 


0-042-t 


23 29 


+ 


700.000 


0-0357 


17 12 




- 200,000 


0-0258 


69 30 


+ 


760,000 


0-0195 


53 




_. 200,000 


0-05G9 


168 18 


+ 


800,000 


0-0039 


140 38 




- 100,000 


0-033-i 


242 56 


-V 


850,000 


0-0144 


176 41 




_ 100.000 


0-0473 


316 IS 


+ 


900,000 


0-0059 


291 10 




_. 50,000 


0-01-31 


50 14 


+ 


900,000 


0-0086 


115 13 










Jl 


,000,000 


0-0628 


67 31 



CLIMATE AND TIME. 





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GEOLOGICAL TIME. 



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CLIMATE AND TIMS. 





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GEOLOGICAL TIME. 



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CLIMATE AND TIME. 





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GEOLOGICAL TIME. 



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I I I 

S I i 



i' OF THE EARTHS ORB 



GEOLOGICAL TIME. 313 

of 200,000 years, constitute the first great period of high 
eccentricity. We then pass onwards for upwards of a million 
and a half years, and we come to the second great period. 
It consists of three maxima separated by two minima. The 
first maximum occurred at 950,000 years ago, the second 
or middle one at 860,000 years ago, and the third and last at 
750,000 years ago — the whole extending over a period of nearly 
300,000 years. Passing onwards for another million and half 
years, or to about 800,000 years in the future, we come to the 
third great period. It also consists of three maxima one huQ« 
dred thousand years apart. These occur at the periods 800,000, 
900,000, and 1,000,000 years to come, respectively, separated 
also by two minima. Those three great periods, two of them 
in the past and one of them in the future, included in the Table, 
are therefore separated from each other by an interval of 
upwards of 1,700,000 years. 

In this Table there are seven periods when the earth's orbit 
becomes nearly circular, four in the past and three in the future. 

The Table shows also four or five subordinate periods of high 
eccentricity, the principal one occurring 200,000 years ago. 

The variations of eccentricity during the four millions of 
years, are represented to the eye diagrammitically in Plate IV. 

In order to determine with more accuracy the condition of 
the earth's orbit during the three periods of great eccentricity 
included in Table I., I computed the values for periods of ten 
thousand years apart, and the results are embodied in Tables 
II., III., and IV. 

There are still eminent astronomers and physicists who are 
of opinion that the climate of the globe never could have been 
seriously afiected by changes in the eccentricity of its orbit. 
This opinion results, no doubt, from viewing the question as a 
purely astronomical one. Viewed from an astronomical stand- 
point, as has been already remarked, there is actually nothing 
from which any one could reasonably conclude with certainty 
whether a change of eccentricity would seriously afiect climate 
or not. By means of astronomy we ascertain the extent of the 



I i 



s = 



§ i I 



I I 
I i 



i I I 



Olff of THt EARTH'S ORB^ 



GEOLOGICAL TIME. 313 

of 200,000 years, constitute the first great period of high 
eccentricity. We then pass onwards for upwards of a million 
and a half years, and we come to the second great period. 
It consists of three maxima separated by two minima. The 
first maximum occurred at 950,000 years ago, the second 
or middle one at 860,000 years ago, and the third and last at 
750,000 years ago — the whole extending over a period of nearly 
300,000 years. Passing onwards for another million and half 
years, or to about 800,000 years in the future, we come to the 
third great period. It also consists of three maxima one hun« 
dred thousand years apart. These occur at the periods 800,000, 
900,000, and 1,000,000 years to come, respectively, separated 
also by two minima. Those three great periods, two of them 
in the past and one of them in the future, included in the Table, 
are therefore separated from each other by an interval of 
upwards of 1,700,000 years. 

In this Table there are seven periods when the earth's orbit 
becomes nearly circular, four in the past and three in the future. 

The Table shows also four or five subordinate periods of high 
eccentricity, the principal one occurring 200,000 years ago. 

The variations of eccentricity during the four millions of 
years, are represented to the eye diagrammitically in Plate IV. 

In order to determine with more accuracy the condition of 
the earth's orbit during the three periods of great eccentricity 
included in Table I., I computed the values for periods of ten 
thousand years apart, and the results are embodied in Tables 
II., III., and IV. 

There are still eminent astronomers and physicists who' are 
of opinion that the climate of the globe never could have been 
seriously afiected by changes in the eccentricity of its orbit. 
This opinion results, no doubt, from viewing the question as a 
purely astronomical one. Viewed from an astronomical stand- 
point, as has been already remarked, there is actually nothing 
from which any one could reasonably conclude with certainty 
whether a change of eccentricity would seriously afiect climate 
or not. By means of astronomy we ascertain the extent of the 



Si6 CLIMATE AND TIME. 

down to ihe sea-leve!, by means of these apparently trifling 
agentSy not only once or twice, but probably dozens of times 
oyer during past ages. Now, when we reflect that with anoh 
extreme slowness do these agents perform their work, that we 
might watch their operations from year to year, and from 
century to century, if we could, without being able to peroeiTO 
that they make any Tery sensible advance, we are necessitated 
to conclude that geological periods must be enormous. And the 
conclusion at which we thus arrive is undoubtedly correct It 
{s, in fact, impossible to form an adequate conception of the 
length of geological time. It is something too vast to be 
fully grasped by our minds. But here we come to the point 
where the fundamental mistake arises ; Geologists do not err 
in forming too great a conception of the extent of geological 
periods, hut in the mode in tchich they represent the length of these 
periods in numbers. When we speak of units, tens, hundreds, 
thousands, we can form some notion of what these quantities 
represent ; but when we come to millions, tens of millions, 
hundreds of millions, thousands of millions, the mind is then 
totally unable to follow, and we can only use these numbers as 
representations of quantities that turn up in calculation. We 
know, £rom the way in which they do turn up in our process of 
calculation, whether they are correct representations of things 
in actual nature or not ; but we could not, from a mere com- 
parison of these quantities with the thing represented by them, 
say whether they were actually too small or too great. 

At present, geologicol estimates of time are little else than 
mere conjectures. Geological science has hitherto afforded no 
trustworthy means of estimating the positive length of geolo- 
gical epochs. Geological phenomena tell us most emphatically 
that these periods must be long; but how long they have 
hitherto failed to inform us. Geological phenomena represent 
time to the mind imder a most striking and imposing form. 
They present to the eye, as it were, a sensuous representation 
of time ; the mind thus becomes deeply impressed with a sense 
of immense duration ; and when one under these feelings is 



GEOLOGICAL TIME. 313 

of 200,000 years, constitute the first great period of high 
eccentricity. We then pass onwards for upwards of a million 
and a half years, and we come to the second great period. 
It consists of three maxima separated by two minima. The 
first maximum occurred at 950,000 years ago, the second 
or middle one at 860,000 years ago, and the third and lust at 
750,000 years ago — the whole extending over a period of nearly 
300,000 years. Passing onwards for another million and half 
years, or to about 800,000 years in the future, we come to the 
third great period. It also consists of three maxima one hun« 
dred thousand years apart. These occur at the periods 800,000, 
900,000, and 1,000,000 years to come, respectively, separated 
also by two minima. Those three great periods, two of them 
in the past and one of them in the future, included in the Table, 
are therefore separated from each other by an interval of 
upwards of 1,700,000 years. 

In this Table there are seven periods when the earth's orbit 
becomes nearly circular, four in the past and three in the future. 

The Table shows also four or five subordinate periods of high 
eccentricity, the principal one occurring 200,000 years ago. 

The variations of eccentricity during the four millions of 
years, are represented to the eye diagrammitically in Plate IV. 

In order to determine with more accuracy the condition of 
the earth's orbit during the three periods of great eccentricity 
included in Table I., I computed the values for periods of ten 
thousand years apart, and the results are embodied in Tables 
II., IIL, and IV. 

There are still eminent astronomers and physicists who are 
of opinion that the climate of the globe never could have been 
seriously afiected by changes in the eccentricity of its orbit. 
This opinion results, no doubt, from viewing the question as a 
purely astronomical one. Viewed from an astronomical stand- 
point, as has been already remarked, there is actually nothing 
from which any one could reasonably conclude with certainty 
whether a change of eccentricity would seriously afiect climate 
or not. By means of astronomy we ascertain the extent of the 



I § I I I I 
! s I I ! i 



i i 



I I I I I 

? s a I I 






GEOLOGICAL TIME. 313 

of 200,000 years, constitute the first great period of high 
eccentricity. We then pass onwards for upwards of a million 
and a half years, and we come to the second great period. 
It consists of three maxima separated by two minima. The 
first maximum occurred at 950,000 years ago, the second 
or middle one at 860,000 years ago, and the third and last at 
750,000 years ago — the whole extending over a period of nearly 
300,000 years. Passing onwards for another million and half 
years, or to about 800,000 years in the future, we come to the 
third great period. It also consists of three maxima one hun« 
dred thousand years apart. These occur at the periods 800,000, 
900,000, and 1,000,000 years to come, respectively, separated 
also by two minima. Those three great periods, two of them 
in the past and one of them in the future, included in the Table, 
are therefore separated from each other by an interval of 
upwards of 1,700,000 years. 

In this Table there are seven periods when the earth's orbit 
becomes nearly circular, four in the past and three in the future. 

The Table shows also four or five subordinate periods of high 
eccentricity, the principal one occurring 200,000 years ago. 

The variations of eccentricity during the four millions of 
years, are represented to the eye diagrammitically in Plate IV. 

In order to determine with more accuracy the condition of 
the earth's orbit during the three periods of great eccentricity 
included in Table I., I computed the values for periods of ten 
thousand years apart, and the results are embodied in Tables 
II., III., and IV. 

There are still eminent astronomers and physicists who' are 
of opinion that the climate of the globe never could have been 
seriously afiected by changes in the eccentricity of its orbit. 
This opinion results, no doubt, from viewing the question as a 
purely astronomical one. Viewed from an astronomical stand- 
point, as has been already remarked, there is actually nothing 
from which any one could reasonably conclude with certainty 
whether a change of eccentricity would seriously afiect climate 
or not. By means of astronomy we ascertain the extent of the 



330 CLIMATE AND TIME. 

of 1865, 1 leamod from him that accurate measurements had 
been made of the amount of sediment annually carried down by 
the Mississippi Biver, full particulars of which investigationfl 
were to be found in the Proceedings of the American Associa- 
tion for the Advancement of Science for 1848. These pro- 
ceedings contain a report by Messrs Brown and Dickeaon, 
which unfortunately over-estimated the amount of sediment 
transported by the Mississippi by nearly four times what was 
afterwards found by Messrs Humphreys and Abbot to be the 
actual amount. From this estimate, I was led to the conclusioix 
that if the Mississippi is a fair representative of rivers in general, 
our existing continents would not remain longer than one 
million and a half years above the sea-level.* This was a con- 
clusion so startling as to excite suspicion that there must have 
been some mistake in reference to Messrs. Brown and Dicke- 
son's data. It showed beyond doubt, however, that the rate of 
subaerial denudation, when accurately determined by this 
method, would be found to be enormously greater than had 
been supposed. Shortly afterwards, on estimating the rate from 
the data furnished by Humphreys and Abbot, I found the rate 
of denudation to be about one foot in 6,000 years. Taking the 
mean elevation of all the land as ascertained by Humboldt to 
be 1,000 feet, the whole would therefore be carried down into 
the ocean by our river systems in about 6,000,000 of years if 
no elevation of the land took placet The following are the 
data and mode of computation by which this conclusion was 
arrived at. It was found by Messrs. Humphreys and Abbot 
that the average amount of sediment held in suspension in the 
waters of the Mississippi is about -^^^ of the weight of the 
water, or ai>W by bulk. The annual discharge of the river is 
19,500,000,000,000 cubic feet of water. The quantity of sediment 
carried down into the Gulf of Mexico amounts to 6,724,000,000 
cubic feet. But besides that which is held in suspension, the 
river pushes down into the sea about 750,000,000 cubic feet of 
earthy matter, making in all a total of 7,474,000,000 cubic ftH3t 

• Phil. Mag. for February, 1867. t Thil. Mag. for May, 1868. 



GEOLOGICAL TIME. 331 

transferred from the land to the sea annually. Whore does 
this enormous mass of material come from P Unquestionably 
it comes from the ground drained by the Mississippi. The area 
drained by the river is 1,244,000 square miles. Now 
7,474,000,000 cubic feet removed off 1,224,000 square mUes of 
surface is equal to \'h% of a foot off that surface per annum, or 
one foot in 4,566 years. The specific gravity of the sediment 
is taken at 1*9, that of rock is about 2*5; consequently the 
amount removed is equal to one foot of rock in about 6,000 
years. The average height of the North American continent 
above the sea-level, according to Humboldt, is 748 feet ; con- 
sequently, at the present rate of denudation, the whole area of 
drainage will be brought down to the sea-level in less than 
4,500,000 years, if no elevation of the land takes place. 

Referring to the above. Sir Charles Lyell makes the follow- 
ing appropriate remarks : — " There seems no danger of our 
overrating the mean rate of waste by selecting the Mississippi 
as our example, for that river drains a country equal to more 
than half the continent of Europe, extends through twenty 
degrees of latitude, and therefore through regions enjoy- 
ing a great variety of climate, and some of its tributaries 
descend from mountains of great height. The Mississippi is 
also more likely to afford us a fair test of ordinary denudation, 
because, unlike the St. Lawrence and its tributaries, there are 
no great lakes in which the fluviatile sediment is thrown down 
and arrested on its way to the sea."* 

The rate of denudation of the area drained by the river 
Ganges is much greater than that of the Mississippi. The 
annual discharge of that river is 6,523,000,000,000 cubic feet 
of water. The sediment held in suspension is equal yIt by 
weight ; area of drainage 432,480 square miles. This gives one 
foot of rock in 2,358 years as the amoimt removed. 

Rouffh estimates have been made of the amount of sediment 
carried down by some eight or ten European rivers; and 
although those estimates cannot be depended upon as being 

♦ Student's "Elemonts of Geology," p. 91. Second Edition. 



J3» 



CUM ATE AND TIME. 



anTthing like perfectly accurate, still tbtoy show (what there is 
very little reason to doubt) that it is extremely probable that 
the European continent is being denuded about as rapidly, as 
the American. 

' For a full account of all that is known on this subject I nmal 
refer to Professor G^ikie's valuable memoir on Modem Denuda- 
tion (Transactions of Qeological Society of Glasgow, yoL iiL ; also 
Jukes and G^ikio's '^ Manual of Geology/' chap, xxv.) It ip 
tnainly through the instrumentality of this luminous and 
exhaustiTC memoir that the method under consideration haa 
gained such wide acceptance amongst geologists. 

Professor G^ikie finds that at the present rate of erosion the 
following is the niunber of years required by the under- 
mentioned rivers to remove one foot of rock from the general 
surface of their basins. Professor Geikie thus shows that the 
rate of denudation, as determined from the amount of sediment 
carried down the Mississippi, is certainly not too high. 

Dnniibe 
MissUaippi 
Nith . 
Ganges 
Hhono . 
Hoong llo 
Po 



6,846 y 


ears. 


6,000 




4J23 




2,358 




1,528 




1,464 




729 





■•s^ 



By means of subaerial agencies continents are being cut up 
into islands, the islands into smaller islands, and so on till the 
whole ultimately disappears. 

No proper estimate has been made of the quantity of sedi* 
ment carried down into the sea by our British rivers. But, 
from the principles just stated, we may infer that it must be 
as great in proportion to the area of drainage as that carried 
down by the Mississippi. For example, the river Tay, which 
drains a great portion of the central Highlands of Scotland^ 
carries to the sea three times as much water in proportion to 
its area of drainage as is carried by the Mississippi. And any 
one who has seen this rapidly running river during a flood, red 
and tui'bid with sediment, will easily be convinced that the 



GEOLOGICAL TIME. 333 

quantity of solid material carriod down by it into the German 
Ocean must be very great. Mr. John Dougall has found that 
the waters of the Clyde during a flood hold in suspension -^^^ 
by bulk of sediment. The observations were made about a 
mile above the city of Glasgow. But even supposing the 
amount of sediment held in suspension by the waters of the 
Tay to be only one-third (which is certainly an under-estimate) 
of that of the Mississippi, viz. -^^js by weight, still this would 
give the rate of denudation of the central Highlands at one 
foot in 6,000 years, or 1,000 feet in 6 millions of years. 

It is remarkable that although so many measurements have 
been made of the amount of fluviatile sediment being transported 
seawards, yet that the bearing which this has on the broad ques* 
tions of geological time and the rate of subaerial denudation 
should have been overlooked. One reason for this, no doubt, is 
that the measurements were made, not with a view to determine 
the rate at which the river basins are being lowered, but mainly 
to ascertain the age of the river deltas and the rate at which 
these are being formed.* 

The Law tchich determines the Mate at which any Country is being 
denuded, — By means of subaerial agencies continents are being 
cut up into islands, the islands into smaller islands, and so on 
till the whole ultimately disappears. 

So long as the present order of things remains, the rate of 
denudation will continue while land remains above the sea-level; 
and we have no warrant for supposing that the rate was during 
past ages less than it is at the present day. It will not do to 
object that, as a considerable amount of the sediment carried 
down by rivers is boulder clay and other materials belonging to 

* In an interesting memoir, published in the Phil. Mag. for 1850, "Mr. Alfred 
Tylor estimated that the basin of the MiMissippi is beinf? lowered at the mte of 
one foot in 10,000 ycfirs by the removal of the Bediment; and he proceeds 
further, and reasons that one foot removed oflf the general surface of the land 
during that period would raise the sea-level three inches. Had it not been that 
Mr. Tylor's attention was directed to the effects produced by the removal of 
sediment in raising the level of the ocean rather than in lowering the level of the 
land, he could not have failed to perceive that he was in possession of a key to 
unfold the mystery of geological time. 



JJ+ CLIMATE AND TIME. 

ihe Ice age, the total amount removed by the riTera ia oil tliai 
aocount greater than it would otherwise be. Were thia objao- 
tion true, it would follow that, prior to the glacial period, wheA 
it is assumed that there was no boulder clay, the £ace of tiba 
country must have consisted of bare rock ; for in this case no 
soil could have accumulated from the disintegration and decom- 
position of the rocks, 9ince^ unless the rocks of a country dismte^ 
grate more rapidly than ihe river syateme are able to carry ik$ 
disintegrated matericUa to the sea, no surface soil can form on thai 
country. The rate at which rivers carry down sediment is 
evidently not determined by the rate at which the rocks are 
disintegrated and decomposed, but by the quantity of rain 
fidling, and the velocity with which it moves off the feoe of 
the country. Every river system possesses a definite amount 
of carrying-power, depending upon the slope of the ground, 
the quantity of rain falling per annum, the manner in which 
the rain falls, whether it falls gradually or in torrents, and a 
few other circumstances. When it so happens, as it generally 
does, that the amount of rock disintegrated on the face of the 
country is greater than the carrying-power of the river systems 
can remove, then a soil necessarily forms. But when the 
reverse is the case no soil can form on that country, and it will 
present nothing but barren rock. This is no doubt the reason 
why in places like the Island of Skye, for example, where the 
rocks are exceedingly hard and difficult to decompose and 
separate, the ground steep, and the quantity of rain falling 
very great, there is so much bare rock to be seen. If, prior 
to the glacial epoch, the rocks of the area drained by the Missis- 
sippi did not produce annually more material from their destruc- 
tion under atmospheric agency than was being carried down by 
that river, then it follows that the country must have presented 
nothing but bare rock, if the amount of rain falling then was 
as great as at present. 

But, after all, one foot removed off the general level of the 
country since the creation of man, according to Mosaic chrono- 
logy, is certainly not a verv great quantity. No person bat 



GEOLOGICAL TIME. 33S 

one who liad some preconcciyed opinions to maintain, would ever 
think of concluding that one foot of soil during 6,000 years was 
an extravagant quantity to be washed off the face of the country 
by rain and floods during that long period. Those who reside 
in the country and are eye-witnesses of the actual effects of heavy 
rains upon the soil, our soft country roads, ditches, brooks, and 
rivers, will have considerable diflBculty in actually believing 
that only one foot has been washed away during the past 6,000 
years. 

Some may probably admit that a foot of soil may be washed 
off during a period so long as 6,000 years, and may tell us that 
what they deny is not that a foot of loose and soft soil, but a 
foot of solid rock can be washed away during that period. But a 
moment's reflection must convince them that, unless the rocks 
of the country were disintegrating and decomposing as rapidly 
into soil as the rain is carrying the soil away, the surface of the 
country would ultimately become bare rock. It is true that 
the surface of our country in many places is protected by a 
thick covering of boulder clay ; but when this has once been 
removed, the rocks will then disintegrate far more rapidly than 
they are doing at present. 

But slow as is the rate at which the country is being de* 
nuded, yet when we take into consideration a period so enor- 
mous as 6 millions of years, we find that the results of denudation 
are really startling. One thousand feet of solid rock during that 
period would be removed from off the face of the country. But 
if the mean level of the country would be lowered 1,000 feet in 
6 millions of years, how much would our valleys and glens be 
deepened during that period ? This is a problem well worthy 
of the consideration of those who treat with ridicule the idea 
that the general features of our country have been carved out 
by subaerial agency. 

In consequence of the retardation of the earth's rotation, 
occasioned by the friction of the tidal-wave, the sea-level must 
be slowly sinking at the equator and rising at the poles. But 
it is probable that the land at the equator is being lowered by 



J36 CLIMATE AND TIME. 

donudation as rapidly as the sea-level is sinking. Nearly am 
mile must have been worn off the equator during the poet 12 milKmu 
of years, if the rate of denudation all along the equator be 
equal to that of the basin of the Ganges. It therefore follows 
that we cannot infer firom the present shape of our globe what 
was its form, or the rate at which it was rotating, at the time 
when its crust became solidified. Although it had been as 
oblate as the planet Jupiter, denudation must in time have 
given it its present form. 

There is another effect which would result from the denuda- 
tion of the equator and the sinking of the ocean at the equator 
and its rise at the poles. This, namely, that it would tend to 
increase the rate of rotation ; or, more properly, it would tend to 
kssen the rate of tidal retardation. 

But if the rate of denudation be at present so great, what 
must it have been during the glacial epoch ? It must have 
been something enormous. At present, denudation is greatly 
retarded by the limited power of our river systems to remove 
the loose materials resulting from the destruction of the rocks. 
These materials accimiulatc and form a thick soil over the sur- 
face of the rocks, which protects them, to a grciit extent, from 
the weathering effects of atmospheric agents. So long as the 
amount of rock disintegrated exceeds that which is being re* 
moved by the river systems, the soil will continue to accumulate 
till the amount of rock destroyed per annum is brought to 
equal that which is being removed. It therefore follows from 
this principle that the CARRYING-po^\^:R of our river systems 
IS THE TRUE MEASURE OF DENUDATION. But during the glacial 
epoch the thickness of the soil would have but little effect in 
diminishing the waste of the rocks; for at that period the 
rocks were not decomposed by atmospheric agency, but were 
ground down by the mechanical friction of the ice. But the 
presence of a thick soil at this period, instead of retarding the 
rate of denudation, would tend to increase it tenfold, for the 
soil would then be used as grinding-material for the ice-sheet. 
In places where the ice was, say, 2,000 feet in thickness, the 



GEOLOGICAL TIME. 337 

ioil would be forced along over the rocky face of the country, 
exerting a pressure on the rocks equal to 50 tons on the square 
foot. 

It is true that the rate at which many kinds of rocks decom* 
pose and disintegrate is far less than what has been concluded 
t<) be the mean rate of denudation of the whole country. This is 
evident from the fact which has been adduced by some writers, 
that inscriptions on stones which have been exposed to atmo- 
spheric agency for a period of 2,000 years or so, have not been 
obliterated. But in most cases epitaphs on monuments and 
tombstones, and inscriptions on the walls of buildings, 200 
years old, can hardly be read. And this is not all : the stone 
on which the letters were cut has during that time rotted in 
probably to the depth of several inches ; and during the course 
of a few centuries more the whole mass will crumble into duet. 

The facts which we have been considering show also how 
trifling is the amount of denudation eflected by the sea in com- 
parison with that by subaerial agents. The entire sea-coast of 
the globe, according to Dr. A. Keith Johnston, is 116,631 
miles. Suppose we take the average height of the coast-line at 
25 feet, and take also the rate at which the sea is advancing on 
the land at one foot in 100 years, then this gives 15,382,600,000 
cubic feet of rock as the total amount removed in 100 years by 
the action of the sea. The total amount of land is 57,600,000 
square miles, or 1,605,750,000,000,000 square feet ; and if one foot 
is removed off* the surface in 6,000 years, then 26,763,000,000,000 
cubic feet is removed by subaerial agency in 100 years, or about 
1,740 times as much as that removed by the sea. Before the 
sea could denude the globe as rapidly as the subaerial agents, 
it would have to advance on the land at the rate of upwards of 
17 feet annually. 

It will not do, however, to measure marine denudation by 
the rate at which the sea is advancing on the land. There is 
no relation whatever between the rate at which the sea is 
advancing on the land and the rate at which the sea is denuding 
the land. For it is evident that as the subaerial agents bring 



J38 CLIMATE AND TIME, 

the coast down to the sea-Ievel, all that the sea has got to do it 
simply to advance, or at most to remove the loose materials 
which may lie in its path. The amount of denudation which 
has been effected by the sea during past geological ages, com- 
pared with what has been effected by subaerial agency, is 
evidently but trifling. Denudation is not the proper function 
of the sea. The great denuding agents are land-ice, frost, rain, 
running- water, chemical agency, &c. The proper work which 
belongs to the sea is the transporting of the loose materials 
carried down by the rivers, and the spreading of these out so 
as to form the stratified beds of fiitur6 ages. 

Pretdous Methods of measunng Gkological Time unreliable. — 
The method which has just been detailed of estimating the rate 
of subaerial denudation seems to afford the only reliable means 
of a geological character of determining geological time in 
absolute measure. The methods which have hitherto been 
adopted not only fail to give the positive length of geological 
periods, but some of them are actually calculated to mislead. 

The common method of calculating the length of a period 
from the thickness of the stratified rocks belonging to that 
period is one of that class. Nothing whatever can be inferred 
from the thickness of a deposit as to the length of time which 
was required to form it. The thickness of a deposit will depend 
upon a greut many circumstances, such as whether the deposi- 
tion took place near to land or far away in the deep recesses of 
the ocean, whether it occurred at the mouth of a great river or 
along the sea-shore, or at a time when tlie sea-bottom was 
rising, subsiding, or remaining stationary. Stratified formations 
10,000 feet in thickness, for example, may, under some condi- 
tions, have been formed in as many years, while under other 
conditions it may have required as many centuries. Nothing 
whatever can be safely inferred as to the absolute length of 
a period from the thickness of the stratified formations belong- 
ing to that period. Neither will this method give us a trust- 
worthy estimate of the relative lengths of geological periods. 
Suppose we find the average thickness of the Cambrian rocks 



GEOLOGICAL TIME. 339 

» be, say, 26,000 feet, the SUurian to be 28,000 feet, the 
Devonian to be 6,000 feet, and the Tertiary to be 10,000 feet, 
it would not be safe to assume, as is sometimes done, that the 
rehttive duration of those periods must have corresponded to 
these numbers. Were we sure that we had got the correct 
average thickness of all the rocks belonging to each of those 
formations, we might probably be able to arrive at the relative 
lengths of those periods ; but we can never be sure of this. 
Those formations all, at one time, formed sea-bottoms ; and we 
can only measure such deposits as are now raised above the 
sea-level. But is not it probable that the relative positions of 
sea and land during the Cambrian, Silurian, Old Red Sandstone, 
Carboniferous, and other early periods of the earth's history, 
differed more trom the present than the distribution of sea and 
land during the Tertiary period differed from that which obtains 
now P May not the greater portion of the Tertiary deposits be 
still under the sea -bottom P And if this be the case, it may 
yet be found at some day in the distant future, when these 
deposits are elevated into dry land, that they are much thicker 
than we now conclude them to be. Of course, it is by no means 
asserted that this is so, but only that they niay be thicker for 
anything we know to the contrary; and the possibility that 
they may, destroys our confidence in the accuracy of this 
method of deteniuning the relative lengths of geological 
periods. 

Neither docs palaqpntology afford any better mode of mea- 
suring geological time. In fact, the palacontological method of 
estimating geological time, either absolute or relative, from the 
rate at which species change, appears to be even still more un- 
satisfactory. If we could ascertain by some means or other the 
time that has elapsed from some given epoch (say, for example, 
the glacial) till the present day, and were we sure at the same 
time that species have changed at a uniform rate during all 
past ages, then, by ascertaining the percentage of change that 
has taken place since the glacial epoch, we should have a means 
of making something like a rough estimate of the lengtli of the 



940 CLIMATE AND TIME. 

▼ariouB periodB. But witlibut some Buch period to start with; 
the paheontological method is useless. It will not do to takA 
the historio period as a base-line. It is &r too short tobe 
used with safety in determining the distance of periods so 
remote as those which concern the geologist. But even sup- 
posing the polseontologist had a period of sufficient length 
measured off correctly to begin with, his results would still be 
unsatis&ctory ; for it is perfectly obvious, that unless the 
climatic conditions of the globe during the yarious periods weire 
nearly the same, the rate at which the species change wotdd 
certainlynot be uniform ; but such has not been the case, as 
an examination of the Tables of eccentricity will show. Take^ 
for example, that long epoch of 260,000 years, beginning about 
980,000 years ago and terminating about 720,000 years ago. 
During that long period the changes from cold to warm condi- 
tions of climate every 10,000 or 12,000 years mudj^hlGive been 
of the most extreme character. Compare that j^jfidd-Wilh the 
period beginning, say, 80,000 years ago, and' ^x^yeading to 
nearly 150,000 years into the future, during which there will 
be no extreme variations of climate, and how great is the oon<- 
trast ! How extensive the changes in species must hav&^bieelx 
during the first period as compared with those which are ifk^y 
to take place during the latter ! 

Besides, it must also be taken into consideration that organi- 
zation was of a far more simple type in the earlier Pala)ozoio 
ages than during the Tertiary period, and would probably on 
this accoimt change much more slowly in the former tlum in 
the latter. 

The foregoing considerations render it highly probable, if 
not certain, that the rate at which the general surface of the 
globe is being lowered by subaerial denudation cannot be much 
under one foot in 6,000 years. Now, if we assign the glacial 
epoch to that period of high eccentricity beginning 980,000 
years ago, and terminating 720,000 years ago, then we must 
conclude that as much as 120 feet must have been denuded off 
the face of the country since the clcse of the glacial epoch. 



GEOLOGICAL TIME. 341 

But if as mucli as this had been carried down yof our rivers 
into the sea, hardly a patch of boulder clay, or any trace of the 
glacial epoch, should be now remaining on the land. It is 
therefore evident that the glacial epoch cannot be assigned to 
that remote period, but ought to be referred to the period ter- 
minating about 80,000 years ago. We have, in this latter case, 
13 feet, equal to about 18 feet of drift, as the amount removed 
from the general surface of the country since the glacial epoch. 
This amount harmonizes very well with the direct evidence of 
geology on this point. Had the amount of denudation since 
the close of the glacial epoch been much greater than this, the 
drift deposits would not only have been far less complete, but 
the general appearance and outline of the surface of all glaciated 
countries would have been very different from what they really are. 
Circumstances which show the Recent Date of the Glacial Epoch. 
— One of the circumstances to which I refer is this. When we 
examine the surface of any glaciated country, such as Scotland, 
we can easily satisfy ourselves that the upper surface of the 
ground differs very much from what it would have been had 
its external features been due to the action of rain and rivers 
and the ordinary agencies which have been at work since the 
close of the Ice period. Go where one will in the Lowlands of 
Scotland, and he shall hardly find a single acre whose upper 
surface bears the marks of being formed by the denuding agents 
which are presently in operation. He will observe everywhere 
moimds and hollows, the existence of which cannot be accounted 
for by the present agencies at work. In fact these agencies 
are slowly denuding pre-existing heights and silting up pre- 
existing hollows. Everywhere one comes upon patches of 
alluvium which upon examination prove to be simply old 
glacially formed hollows silted up. True, the main rivers, 
streams, and even brooks, occupy channels which have been 
formed by running water, either since or prior to the glacial 
epoch, but, in regard to the general surface of the country, 
the present agencies may be said to be just beginning to carve 
a new line of features out of the old glacially formed surfaco. 



34S CLIMATE AND TIME. 

But 00 little progress lias yet been made, that the ksreflai 
gravel mounds, knolls of boulder day, &c.y still retain in moat 
cases their original form. Now, when we reflect that mora 
than a foot of drift is being removed from the general siir&oe 
of the country every 6,000 years or so, it becomes perleotlj 
obvious that the close of the glacial epoch must be of compara- 
tively recent date. 

There is another circumstance which shows that the glacial 
epoch must be referred to the latest period of great eccentricity. 
If we refer the glacial epoch to the penultimate period of ex- 
treme eccentricity, and place its commencement one million of 
years back, then we must also lengthen out to a correqxmding 
extent the entire geological history of the globe. Sir Charles 
Lyell, who is inclined to assign the glacial epoch to this 
penultimate period, considers that when we go back as fiur as 
the Lower Miocene formations, we arrive at a period wh^i the 
marine shells differed as a whole from those now existing. But 
only 6 percent, of the shells existing at the commencement of the 
glacial epoch have since died out. Hence, assuming the rate at 
which the species change to be uniform, it follows that the Lower 
Miocene period must be twenty times as remote as the commence- 
ment of the glacial epoch. Consequently, if it be one million of 
years since the commencement of the glacial epoch, 20 millions 
of years. Sir Charles concludes, must have elapsed since the time 
of the Lower Miocene period, and 60 millions of years since 
the beginning of the Eocene period, and about 160 millions of 
years since the Carboniferous period, and about 240 millions 
of years must be the time which has elapsed since the begin- 
ning of the Cambrian period. But, on the other hand, if we 
refer the glacial epoch to the latest period of great eccentricity, 
and take ^50,000 years ago as the beginning of that period, 
then, according to the same mode of calculation, we have 15 
millions of years since the beginning of the Eocene period, 
and 40 millions of years since the Carboniferous period, and 
60 millions of years in all since the beginning of the Cambrian 
period. 



GEOLOGICAL TIME. ^i 

If the beginning of the glacial epoch be carried back a 
million years, then it is probable, as Sir Charles Lyell con- 
cludes, that the beginning of the Cambrian period will require 
to be placed 240 millions of years back. But it is very pro- 
bable that the length of time embraced by the pre-Cambrian 
ages of geological history may be as great as that which has 
elapsed since the close of the Cambrian period, and, if this be 
so, then we shall be compelled to admit that nearly 500 millions 
of years have passed away since the beginning of the earth's 
geological history. But we have evidence of a physical nature 
which proves that it is absolutely impossible that the existing 
order of things, as regards our globe, can date so far back as 
anything like 500 millions of years. The arguments to which 
I refer are those which have been advanced by Professor 
Sir William Thomson at various times. These arguments are 
well known, and to all who have really given duo attention to 
them must be felt to be conclusive. It would be superfluous 
to state them horo ; I shall, however, for reasons which will 
presently appear, refer briefly to one of them, and that one 
which seems to be the most conclusive of all, viz., the argument 
derived from the limit to the age of the sun's heat. 

Professor Ramsay on Geological Time. — In an interesting 
suggestive memoir, "On Geological Ages as items of Geo- 
logical Time,"* Professor Ramsay discusses the comparative 
values of certain groups of formations as representative of 
geological time, and arrives at the following general conclusion, 
viz., "That the local continental era which began with the 
Old Red Sandstone and closed with the New Red Marl is com- 
parable, in point of geological time, to that occupied in the 
deposition of the whole of the Mesozoic, or Secondary series, 
later than the New Red Marl and all the Cainozoic or Tertiary 
formations, and indeed of all the time that has elapsed since 
the beginning of the deposition of the Lias down to the present 
day.'* This conclusion is derived partly from a comparison of 
the physical character of the formations constituting each 

• Proc. Boy. Soc, No. 162, 1874. 

16 



544 CLIMATE AND TIME. 

group, but principaUj from the zoological changeB which took 
place during the time represented bj them. 

The earlier period represented by the Cambrian and Siliixiaa 
rocks he also, from the same considerations^ considers to haTS 
been very long, but he does not attempt to fix its relative 
length. Of the absolut<e length of any or all of these great 
eras of geological time no estimate or guess is giren. He 
believesy however, that the whole time represented by all the 
fossiliferous rocks, from the earliest Cambrian to the most 
recent, is, geologically speaking, short compared with that 
which went before it. After quoting Professor Huxley's 
enumeration of the many classes and orders of marine life 
(identical with those still existing), whose remains characteriie 
the lowest Cambrian rocks, he says, " The inference is obvious 
that in this earliest known varied life we find no evidence of 
its having lived near the beginning of the zoological series. 
In a broad sense, compared with what must have gone before, 
both biologically and physically, all the phenomena connected 
with this old period seem to my mind to be quite of a recent 
description, and the climates of seas and lands were of the very 
same kind as those that the world enjoys at the present day/' 
. . . " In the words of Darwin, when discussing the imper- 
fection of the geological record of this history, * we possess the 
last volume alone relating only to two or three countries,' and 
the reason why we know so little of pre-Cambrian faunas and 
the physical characters of the more ancient formations as origi- 
nally deposited, is that below the Cambrian strata we get at 
onc^ involved in a sort of chaos of metamorphic strata.' " 

It seems to me that Professor Ramsay's results lead to the 
same conclusion regarding the positive length of geological 
periods as those derived from physical considerations. It is 
true that his views lead us back to an immense lapse of unknown 
time prior to the Cambrian period, but this practically tends 
to shorten geological periods. For it is evident that the geo- 
logical history of our globe must be limited by the age of the 
sun's heat, no matter how long or short its age may bei This 



GEOLOGICAL TIME. 



345 



being the case, the greater the length of time which must have 
elapsed prior to the Cambrian period, the less must be the time 
which has elapsed since that period. Whatever is added to 
the one period must be so much taken from the other. Conse- 
quently, the longer we suppose the pre-Cambrian periods to 
have been, the shorter must we suppose the post-Cambrian 
to be. 



/ 



cnBAPTEB xn. 

THE FROBABLB AGS AND ORIGIN OF THE SUIT. 

3imYitation Theory. — Amount of Heat emitted bj the San. — ^Meteoric Theoiy. 
— Helmholtn's Condeniation Theory. — Confusion of Ideaa.— Gravitation not 
the chief Source of the Son's Heat. — Originid Heat. — Souroe of Original 
Heat. — Original Heat derived from Motion in Space. — Conclanon aa to 
Bate of Glacial Epoch. — False Analogy. — Probable Date of Eocene and 
l^liocene Periods. 

Graatatton Theory of tJie Origin and Source of the Sun's JETeat. 
—-There are two fonns in which this theory has been presented: 
the first, the meteoric theory, propounded by Dr. Meyer, of 
Heilbronn ; and the second, the contraction theory, advocated 
by Hehnholtz. 

It is found that 83*4 foot-pounds of heat per second are 
incident upon a square foot of the earth's surface exposed to 
the perpendicular rays of the sun. The amount radiated from 
a square foot of the sun's surface is to that incident on a square 
foot of the earth's surface as the square of the sun's distance to 
the square of his radius, or as 46,400 to 1. Consequently 
3,869,000 foot-pounds of heat are radiated off every square 
foot of the sun's surface per second — an amount equal to about 
7,000 horse power. The total amount radiated from the whole 
surface of the sun per annum is 8,340 x 10^ foot-pounds. To 
maintain the present rate of radiation, it would require the 
combustion of about 1,600 lbs. of coal per hour on every square 
foot of the sun's surface ; and were the sun composed of that 
material, it would be all consumed in less than 5,000 years. 
The opinion that the sun's heat is maintained by combustion 
cannot be entertained for a single moment. A pound of coal 
falling into the sun from an infinite distance would produce bj 



GEOLOGICAL TIME. 347 

its concussion more than 6,000 times the amount of heat that 
would be generated by its combustion. 

It is well known that the velocity with which a body falling 
from an infinite distance would reach the sun would be equal 
to that which would be generated by a constant force equal to 
the weight of the body at the sun's surface operating through a 
space equal to the sun's radius. One pound would at the sun'a 
surface weigh about 28 pounds. Taking the sun's radius at 
441,000 miles,* the energy of a pound of matter falling into 
the sun from infinite space would equal that of a 28-pound 
weight descending upon the earth from an elevation of 441^000 
miles, supposing the force of gravity to be as great at that 
elevation as it is at the earth's surface. It would amount to 
upwards of 65,000,000,000 foot-pounds. A better idea of thia 
enormous amount of energy exerted by a one-pound weight 
falling into the sun will be conveyed by stating that it would 
be sufficient to raise 1,000 tons to a height of 6| miles. It 
would project the Warrior y fully equipped with guns, stores, 
and ammunition, over the top of Ben Nevis. 

Gravitation is now generally admitted to be the only con- 
ceivable source of the sim's heat. But if we attribute the 
energy of the sun to gravitation as a source, we assign it to a 
cause the value of which can be accurately determined. Pro- 
digious as is the energy of a single pound of matter falling 
into the sun, nevertheless a range of mountains, consisting of 
176 cubic miles of solid rock, falling into the sun, would main- 
tain his heat for only a single second. A mass equal to that 
of the earth would maintain the heat for only 93 years, and a 
mass equal to that of the sun itself falling into the sun would 
afford but 33,000,000 years' sun-heat. 

It is quite possible, however, that a meteor may reach the 
sun with a velocity far greater than that which it could acquire 
by gravitation ; for it might have been moving in a direct line 
towards the sun with an original velocity before coming under 

* I have taken for the volume and mass of the sun the values given in Pro- 
fatoor Sir William Thomson's memoir, PhiL Mag., vol. viii. (18^4) 



MS CLIMATE AND TIME. 

the Benaible inflaenoe of the buh'b attraotion* In thii mm a 
greater amount of heat would be generated by the metaor tihan 
would have resulted from its merely &lling into the sun imder 
the influence of gravitation. But then meteors of this sort 
must be of rare occurrence. The meteorio theory of the son's 
heat has now been pretty generally abandoned for the oontrso* 
tion theory advanced by Helmholtz. 

Suppose^ with Helmholtz, that the sun originally existed ss 
a nebulous mass, filling the entire space presently oooupied by 
the solar system and extending into space indefinitely beyond 
the outermost planet. The total amount of work in foot-pounds 
performed by gravitation in the condensation of this mass to 
an orb of the sun's present size can be found by means of tbs 
following formula given by Helmholtz,* 

Work of condensation = .- . ^^ . g 

• 

M is the moss of the sun, m the mass of the earth, It the sun's 
radius, and r the earth's radius. Taking M = 4230 x KPlbs., 
m = 11,920 X 10*^ lbs., R = 2,328,600,000 feet, and r » 
20,889,272 feet ; we have then for the total amoimt of work 
performed by gravitation in foot-pounds. 

Work = ' . (20,889,272-6)« x (4230 X lO*')' 
6 2,328.600,000 X 11,920 X 10" " 
= 168,790 X 103« foot-pounda. 

The amount of heat thus produced by gravitation would suffice 
for nearly 20,237,500 years. 

These calculations are based upon the assumption that the 
density of the sun is uniform throughout. But it is highly 
probable that the sun's density increases towards the centre, 
in which case the amount of work performed by gravitation 
would be somewhat more than the above. 

Some confusion has arisen in reference to this subject by the 
introduction of the question of the amount of the sun's specifio 
heat. If we simply consider the sun as an incandescent body 

• FhiL Mag., { 4, toI. xL, p. 616 (1866). 



GEOLOGICAL TIME. 349 

in the process of cooling, the question of the amount of the 
sun's specific heat is of the utmost importance ; because the 
absolute amount of heat which the sun is capable of giving out 
depends wholly upon his temperature and specific heat. In 
this case three things only are required : (1), the sun's mass ; 
(2), temperature of the mass ; (3), specific heat of the mass. 
But if we are considering what is the absolute amount of heat 
which could have been given out by the sun on the hypothesis 
that gravitation, either according to the meteoric theory 
suggested by Meyer or according to the contraction theory 
advocated by Helmholtz, is the only source of his heat, then 
we have nothing whatever to do with any inquiries regarding 
the specific heat of the sun. This is evident because the abso- 
lute amount of work which gravitation can perform in the 
pulling of the particles of the sun's mass together, is wholly 
independent of the specific heat of those particles. Conse- 
quently, the amount of energy in the form of heat thus 
imparted to the particles by gravity must also be wholly 
independent of specific heat. That is to say, the amount of 
heat imparted to a particle will be the same whatever may be 
its specific heat. 

Even supposing we limit the geological history of our globe 
to 100 millions of years, it is nevertheless evident that gravita- 
tion will not account for the supply of the sun's heat during 00 
long a period. There must be some other source of much more 
importance than gravitation. What other source of energy 
greater than that of gravitation can there be P It is singular 
that the opinion should have become so common even among 
physicists, that there is no other conceivable source than gravi- 
tation from which a greater amount of heat could have been 
derived. 

The Origin and Chief Source of tlie Sun's Heat, — According 
to the foregoing theories regarding the source of the sun's heat, 
it is assumed that the matter composing the sim, when it 
existed in space as a nebulous mass, was not originally pos- 
sessed of temperature, but that the temperature was given to it 



350 CLIMATE AND TIME. 

as the mass became condensed under the force of grayitation. 
It is supposed that the heat given out was simply the heat of 
condensation. But it is quite conceivable that the nebulous 
mass might have been possessed of an original store of heat 
previous to condensation. 

It is quite possible that the very reason why it existed in 
such a rarefied or gaseous condition was its excessive tem- 
perature, and that condensation only began to take place when 
the mass began to cool down. It seems far more probable that 
this should have been the case than that the mass existed in so 
rarefied a condition without temperature. For why should the 
particles have existed in this separated form when devoid of the 
repulsive energy of heat, seeing that in virtue of gravitation 
they had such a tendency to approach to one another ? But if 
the mass was originally in a heated condition, then in con- 
densing it would have to part not only with the heat generated 
in condensing, but also with the heat which it originally pos- 
sessed, a quantity which would no doubt much exceed that 
produced by condensation. To illustrate this principle, let us 
suppose a pound of air, for example, to be placed in a cylinder 
and heat applied to it. If the piston be so fixed that it cannot 
move, 234*5 foot-pounds of heat will raise the temperature of 
the air 1° C. But if the piston be allowed to rise as the heat 
is applied, then it will require 330-2 foot-pounds of heat to 
raise the temperature 1° C. It requires 95*7 foot-pounds more 
heat in the latter case than in the former. The same amount 
of energy, viz., 234*5 foot-pounds, in both cases goes to produce 
temperature ; but in the latter case, where the piston is allowed 
to move, 95*7 foot-pounds of additional heat arc consumed in 
the mechanical work of raising the piston. Suppose, now, that 
the air is allowed to cool under the same conditions : in the one 
case 234*5 foot-pounds of heat will bo given out while the tem- 
perature of the air sinks 1^ 0. ; in the other case, where the 
piston is allowed to descend, 330*2 foot-pounds wUl be given 
out while the temperature sinks 1° C. In the former case, the 
air in cooling has simply to part with the energy which it po^- 



GEOLOGICAL TIME. JSI 

Besses in the form of temperature ; but in the latter case it has, 
in addition to this, to part with the energy bestowed upon its 
molecules by the descending piston. While the temperature 
of the gas is sinking 1°, 95*7 foot-pounds of energy in the 
form of heat are being imparted to it by the descending piston ; 
and these have to be got rid of before the temperature is lowered 
by 1°. Consequently 234*5 foot-pounds of the heat given out 
previously existed in the air under the form of temperature, 
and the remaining 95*7 foot-pounds given out were imparted 
to the air by the descending piston while the gas was losing 
its temperature. 234*5 foot-pounds represent the energy or 
heat which the air previously possessed, and 95*7 the energy or 
heat of condensation. 

In the case of the cooling of the sun from a nebulous mass, 
there would of course be no external force or pressure exerted 
on the mass analogous io that of the piston on the air ; but 
there would be, what is equivalent to the same, the gravitation 
of the particles to each other. There would be the pressure of 
the whole mass towards the centre of convergence. In the 
case of air, and all perfect gases cooling under pressure, about 
234 foot-poimds of the original heat possessed by the gas are 
given out while 95 foot-pounds are being generated by con- 
densation. We have, however, no reason whatever to believe 
that in the case of the cooling of the sun the same proportions 
would hold true. The proportion of original heat possessed by 
the mass of the sun to that produced by condensation may have 
been much greater than 234 to 95, or it may have been much 
less. In the absence of all knowledge on this point, we may 
in the meantime assume that to be the proportion. The total 
quantity of heat given out by the sun resulting from the con- 
densation of his mass, on the supposition that the density of 
the sun is imiform throughout, we have seen to be equal to 
20,237,500 years' sun-heat. Then the quantity of heat given 
out, which previously existed in the mass as original tempera- 
ture, must have been 49,850,000 years' heat, making in all 
70,087,500 years' heat as the total amount. 




±m^ 



■CfXL 



- 5Il!rr» 



;• *- 







I_:"<^ iZL>c*» : 




:f>"-.iiii- * 



GEOLOGICAL TIME. 353 

What power could have communicated to tlie mass 50|000^000 
years' heat before condensation began to take place P 

The Sun's Energy may have originally been derived from Motion 
in Space, — There is nothing at all absurd or improbable in the 
supposition that such an amount of energy might have been 
commimicated to the mass. The D3mamical Theory of Heat 
affords an easy explanation of at least how such an amount of 
energy may have been commimicated. Two bodies, each one- 
half the mass of the sun, moving directly towards each other 
with a velocity of 476 miles per second, would by their concus- 
sion generate in a single moment the 50,000,000 years' heat. 
For two bodies of that mass moving with a velocity of 476 
miles per second would possess 4149 x 10^ foot-pounds of 
energy in the form of vis viva ; and this, converted into heat by 
the stoppage of their motion, would give an amount of heat 
which would cover the present rate of the sun's radiation, for a 
period of 50,000,000 years. 

Why may not the sun have been composed of two such 
bodies P And why may not the original store of heat possessed 
by him have all been derived from the concussion of these two 
bodies P Two such bodies coming into collision with that 
velocity would be dissipated into vapour by such an incon- 
ceivable amount of heat as would thus be generated ; and when 
they condensed on cooling, they would form one spherical mass 
like the sun. It is perfectly true that two such bodies could 
never attain the required amount of velocity by their mutual 
gravitation towards each other. But there is no necessity 
whatever for supposing that their velocities were derived from 
their mutual attraction alone. They might have been approach- 
ing towards each other with the required velocity wholly inde- 
pendent of gravitation. 

We know nothing whatever regarding the absolute motion 
of bodies in space. And beyond the limited sphere of our 
observation, we know nothing even of their relative motions. 
There may be bodies moving in relation to our system with 
inconceivable velocity. For anything that we know to th€ 



SH CLIMATE AND TIME. 



I 



eoniaraiy, were one of these bodies to strike our earthy th« 
shock might be sufficient to generate an amount of heat that 
would dissipate the earth into yapouri though the striking 
body might not be heavier than a cannon-ball. There is, how- 
ever, nothing very extraordinary in the velocity which wo 
have found would be required in the two supposed bodies to 
generate the 50,000,000 years' heat. A comet, having an orbit 
extending to the path of the planet Neptune, approaching so 
near the sun as to almost graze his surface in passing, would 
have a velocity of about 390 miles per second, which is within 
86 miles of the required velocity. 

But in the original heating and expansion of the sun into a 
gaseous mass, an amount of work must have been performed 
against gravitation equal to that which has been performed by 
gravitation during his cooling and condensation, a quanti^ 
which we have found amounts to about 20,000,000 years' heat. 
The total amount of energy originally communicated by the con- 
cussion must have been equal to 70,000,000 years' sun-heat. A 
velocity of 563 miles per second would give this amount. It must 
be borne in mind, however, that the 503 miles per second is the 
velocity at the moment of collision ; about one-half of this 
velocity would be derived from the mutual attraction of the 
two bodies in their approach to each other. Suppose each 
body to be equal in volume to the sun, and of course one-half 
the density, the amount of velocity which they would acquire 
by their mutual attraction would be 274 miles per second, con"> 
■equently we have to assume an original or projected velocity 
of only 289 miles per second. 

If we admit that gravitation is not sufficient to account for 
the amount of heat given out by the sun during the geological 
history of our globe, we are compelled to assume that the mass 
of which the sun is composed existed prior to condensation in a 
heated condition; and if so, we are further obliged to admit that 
the mass must have received its heat from some source or other. 
And as the dissipation of heat into space must have been going 
on, in all probability, as rapidly before as after condensation 



GEOLOGICAL TIME. 355 

took place, we are further obliged to conclude that the heat 
must have been communicated to the mass immediately before 
condensation began, for the moment the mass began to lose its 
heat condensation would ensue. If we confine our speculations 
to causes and agencies known to exist, the cause which has 
been assigned appears to be the only conceivable one that will 
account for the production of such an enormous amount of heat. 

The general conclusion to which we are therefore led from 
physical considerations regarding the age of the sim's heat is, 
that the entire geological history of our globe must be com- 
prised within less than 100 millions of years, and that conse* 
quently the commencement of the glacial epoch cannot date 
much farther back than 240,000 years. 

The facts of geology, more especially those in connection 
with denudation, seem to geologists to require a period of much 
longer duration than 100 millions of years, and it is this which 
has so long prevented them accepting the conclusions of physical 
science in regard to the age of our globe. But the method of 
measuring subaerial denudation already detailed seems to me 
to show convincingly that the geological data, when properly 
interpreted, are in perfect accord with the deductions of physical 
science. Perhaps there are now few who have fairly considered 
the question who will refiise to admit that 100 millions of 
years are amply sufficient to comprise the whole geological his- 
tory of our globe. 

A fake Analogy supposed to exist between Astronomy and 
Geology. — Perhaps one of the things which has tended to mis- 
lead on this point is a false analogy which is supposed to sub- 
sist between astronomy and geology, viz., that geology deals 
with unlimited timey as astronomy deals with unlimited space. 
A little consideration, however, will show that there is not 
much analogy between the two cases. 

Astronomy deals with the countless worlds which lie spread 
out in the boimdless infinity of space ; but geology deals with 
only one world. No doubt reason and analogy both favour the 
idea that the age of the material universe, like its magnitude. 



156 CLIMATE AND TIME. 

ib immeasurable ; we have no reason, howeyer, to oondiide thiil 
it is eternal, any more than we have to infer that it is infinitsi 
But when we compare the age of the material universe with its 
magnitudoi we must not take the age of one of its members 
(say, our globe) and compare it with the size of the univeorae. 
Neither must we compare the age of all the presently existing 
systems of worlds with the magnitude of the universe ; but we 
must compare the past history of the universe as it stretches 
back into the immensity of bygone time^ with the presently 
existing universe as it stretches out on all sides into limitless 
ipaee. For worlds precede worlds in time as worlds lie beyond 
worlds in space. Each world, each individual, each atom is 
evidently working out a final purpose, according to a plan pre- 
arranged and predetermined by the Divine Mind from all 
eternity. And each world, like each individual, when it serves 
the end for which it was called into existence, disappears to 
make room for others. This is the grand conception of the 
universe which naturally impresses itself on every thoughtful 
mind that has not got into confusion about those things called 
in science the Laws of Nature.* 

But the geologist does not pass back &om world to world as 
they stand related to each other in the order of succession in timet 
as the astronomer passes from world to world as they stand 
related to each other in the order of coexistence in space. The 
researches of the geologist, moreover, are not only confined to 
one world, but it is only a portion of the history of that one 
world that can come under his observation. The oldest of 
existing formations, so far as is yet known, the Laurentian 
Gneiss, is made up of the waste of previously existing rocks, 
and it, again, has probably been derived from the degradation 
of rocks belonging to some still older period. Regarding what 
succeeds these old Laurentian rocks geology tells us much ; but 
of the formations that preceded, we know nothing whatever. 
For anything that geology shows to the contrary, the time 
which mny have elapsed from the solidifying of the earth's 

• Phil. Mag. f )r July, 1872, p. 1. 



GEOLOGICAL TIME. 357 

enist to the deposition of tlie Laurentian strata — an absolute 
blank — may have been as great as the time that has since in- 
tervened. 

Probable Date of the Eocene and Miocene Periods, — If we take 
into consideration the limit which physical science assigns to 
the age of our globe, and the rapid rate at which, as we have 
seen, denudation takes place, it becomes evident that the enor- 
mous period of 3 millions of years comprehended in the fore- 
going tables must stretch far back into the Tertiary age. 
Supposing that the mean rate of denudation during that period 
was not greater than the present rate of denudation, still we 
should have no less than 500 feet of rock worn off the face of 
the country and carried into the sea during these 3 millions 
of years. This fact shows how totally diflFerent the appearance 
and configuration of the country in all probability was at the 
commencement of this period from what it is at the present day. 
If it be correct that the glacial epoch residted from the causes 
which we have already discussed, those tables ought to aid us 
in our endeavour to ascertain how much of the Tertiary period 
may be comprehended within these 3 millions of years. 

We have already seen (Chapter XVIII.) that there is evidence 
of a glacial condition of climate at two different periods during 
the Tertiary age, namely, about the middle of the Miocene and 
Eocene periods respectively. As has already been shown, the 
more severe a glacial epoch is, the more marked ought to be 
the character of its warm inter- glacial periods ; the greater the 
extension of the ice during the cold periods of a glacial epoch 
the further should that ice disappear in arctic regions during 
the corresponding warm periods. Thus the severity of a glacial 
epoch may in this case be indirectly inferred from the character 
of the warm periods and the extent to which the ice may have 
disappeared from arctic regions. Judged by this test, we have 
every reason to believe that the Miocene glacial epoch was one 
of extreme severity. 

The Eocene conglomerate, devoid of all organic remains, and 
containing numerous enormous ice- transported blocks, is, as we 



iS» CLIMATE AND TIME. 

have seeiii immediately associated with nummnlitic strata duurgod 
with fossils characteristic of a warm climate. Befening to 
this Sir Charles Lyell says, ''To imagine icebergs carrying 
such huge fragmenta of stone in so southern a latitude, and at 
a period immediately preceded and followed by the signs of a 
warm climate, is one of the most perplexing enigmas whioh 
the geologist has yet been called upon to solve."* 

It is perfectly true that, according to the generally received 
theories of the cause of a glacial climate the whole is a perplex* 
ing enigma, but if we adopt the Secular theory of change of 
clunate, every difficulty disappears. According to this theory the 
▼ery £ict of the conglomerate being formed at a period imme* 
diately preceded and succeeded by warm conditions of climate, is 
of itself strong presumptive evidence of the conglomerate being 
a glacial formation. But this is not all, the very highness 
of the temperature of the preceding and succeeding periods 
bears testimony to the severity of the intervening glacial 
period. Despite the deficiency of direct evidence regarding the 
character of the Miocene and Eocene glacial periods, we are 
not warranted, for reasons which have been stated in Chapter 
XYIL, to conclude that these periods were less severe than 
the one which happened in Quaternary times. Judging from 
indirect evidence, we have some groimds for concluding that 
the Miocene glacial epoch at least was even more seyere and 
protracted than our recent glacial epoch. 

By referring to Table I., or the accompanying diagram, it 
will be seen that prior to the period which I have assigned as 
that of the glacial epoch, there are two periods when the 
eocentricity almost attained its superior limit. The first period 
occurred 2,500,000 years ago, when it reached 0*0721, and the 
second period 850,000 years ago, when it attained a still higher 
▼alue, viz., 0*0747, being within 0*0028 of the superior limit. 
To the first of these periods I am disposed to assign the glacial 
epoch of Eocene times, and to the second that of the Miocene 
age. With the view of determining the character of these 

" Prindplet,*' p. 210. Eleventh Edition. 



GEOLOGICAL TIME. 359 

periods Tables II. and HI. have been computed. They give 
the eccentricity and longitude of penhelion at intervals of 
10,000 years. It will be seen from Table II. that the Eocene 
period extends from about 2,620,000 to about 2,460,000 years 
ago ; and from Table III. it will be gathered that the Miocene 
period lasted from about 980,000 to about 720,000 years ago. 

In order to find whether the eccentricity attained a higher 
value about 850,000 years ago than 0*0747, I computed the 
values for one or two periods immediately before and after that 
period, and satisfied myself that the value stated was indeed 
the highest, as will be seen from the subjoined table : — 



851,000 


007454 


850,000 


0-074664 


849,500 


0-07466 


840,000 


007466 



How totally difierent must have been the condition of the 
earth's climate at that period from what it is at present! 
Taking the mean distance of the sun to be 91,400,000 miles, 
his present distance at mid- winter is 89,864,480 miles ; but at 
the period in question, when the winter solstice was in peri- 
helion, his distance at mid-winter would be no less than 
98,224,289 miles. But this is not all; our winters are at 
present shorter than our summers by 7*8 days, but at that period 
they would be longer than the summers by 34*7 days. 

At present the difference between the perihelion and aphelion 
distance of the sun amounts to only 3,069,580 miles, but at the 
period under consideration it would amount to no less than 
13,648,679 miles I 



CHAPTER XXTT, 

A MBTHOD OF DETERMINING THE MEAN THICKNESS OF 
SEDIMENTARY ROCKS OF THE GLOBE. 

Prevniling Methods defectiTe. — Mazimam Tkiclmesa of British Rooki. — ^ThiM 
Kluments in the Question. — ^l^rofeesor Hnzltry on the Bate of Depotitioiiw— • 
ThickneM of Stfdimentary Rocks enormously over-estimated. — Oheerrad 
Thickness no Measure of moan Thickness. — Deposition of Sediment prinoi- 
xMy uloiiff Si'U-inur^n. — Mistaken Iiiferencb regarding the Absence of a 
ronnatiou. — Immoiuto Antiquity of existing Ocoauii. 

Various attempts have been mode to measure the positive 
length of geological periods. Some geologists have sought to 
determiae, roughly, the age of the stratified rocks by calcula- 
tions based upon their probable thickness and the rate at which 
they may have been deposited. This methodi howeveri is 
worthless, because the rates which have been adopted are purely 
arbitrary. One geologist will take the rate of deposit at a 
fuot in a hundred years, while another will assume it to be a 
foot in a thousand or perhaps ten thousand years ; and, for any 
reasons that have been assigned, the one rate is just as likely to 
be correct as the other : for if we examine what is taking place 
in the ocean bed at the present day, we shall find in some places 
a foot of sediment laid down in a year, while in other places a 
foot may not be deposited in a thousand years. The stratified 
rocks wero evidently formed at all pos^sible rates. When we 
speak of the rate of their formation, we must of course refer to 
the tnean rate ; and it is perfectly true that if we knew the 
thickness of these rocks and the mean rate at wliich they were 
deposited, wo should have a ready means of determining their 
positive ago. lint there appears to be nearly as great uncer- 
tainty regaixling the thickness of the scnlimcntary rocks aa 



THICKNESS OF SEDIMENTARY ROCKS. 361 

regarding the rate at which they were formed. No doubt we 
can roughly estimate their probable maximum .thickness ; for 
instance, Professor Kamsay has found from actual measurement, 
that the sedimentary formations of Great Britain have a maxi- 
mum thickness of upwards of 72,000 feet ; but all such measure- 
ments give us no idea of their mean thickness. What is the mean 
thickness of the sedimentary rocks of the globe P On this point 
geology does not afford a definite answer. Whatever the 
present mean thickness of the sedimentary rocks of our globe 
may be, it must be small in comparison to the mean thickness 
of all the sedimentary rocks which have been formed. This ia 
obvious from the fact that the sedimentary rocks of one age are 
partly formed from the destruction of the sedimentary rocks of 
former ages. From the Laurentian age down to the present 
day, the stratified rocks have been xmdergoing constant denu- 
dation. 

Unless we take into consideration the quantity of, rock 
removed during past ages by denudation, we cannot — even 
though we knew the actual mean thickness of the existing 
sedimentary rocks of the globe, and the rate at which they 
were formed — arrive at an estimate regarding the length of 
time represented by these rocks. For if we are to determine 
the age of the stratified rocks from the rate at which they were 
formed, we must have, not the present quantity of sedimentary 
rocks, but the present plus the quantity which has been 
denuded during past ages. In other words, we must have the 
absolute quantity formed. In many places the missing beds 
must have been of enormous thickness. The time represented 
by beds which have disappeared is, doubtless, as already re- 
marked, much greater than that represented by the beds which 
now remain. The greater mass of the sedimentary rocks has 
been formed out of previously existing sedimentary rocks, and 
those again out of sedimentary rocks still older. As the ma- 
terials composing our stratified beds may have passed through 
many cycles of destruction and re-formation, the time required 
to have deposited at a given rate the present existing mass of 



36s CLIMATE AND TIME. 

aedimentary rocks may be but a fraction of the timie reqtnzed 
to baye depoaited at tbe Bame rate ibe total maaa tbat hu 
aotually been formed. To measure tbe age of tbe aedimentarj 
rocks by tbe present existing rocks, assumed to be formed wX 
some given rate, even supposing tbe rate to be correct^ is a 
loetbod wbdly fallaioious. 

" Tbe aggregate of sedimentary strata in tbe eartb'a crust,'* 
says Sir Cbarles Lyelli '' can never exceed in volume ibe amoant 
of solid matter wbicb bas been ground down and wasbed away 
by rivers, waves, and currents. How vast, tben» must be the 
spaces wbicb ibis abstraction of matter bas left vacant 1 How 
&r exceeding in dimensions all tbe valleys, bowever numerous 
sad tbe boUows, bowever vast, wbicb we can prove to bave 
been cleared out by aqueous erosion ! " ♦ 

I presume there are few geologists who would not admit tbat if 
all tbe rocks wbicb have in past ages been removed by denuda- 
tion were restored, the mean thickness of the sedimentary rocks 
of tbe globe would be at least equal to their present maximum 
thickness, which we may take at 72,000 feet. 

There are three elements in the question ; of which if two 
are known, the third is known in terms of the other two. If 
we have the mean thickness of all the sedimentary rocks wbicb 
have been formed and the mean rate of formation, then we 
bave the time which elapsed during the formation ; or having 
the thickness and the time, we have the rate ; or, having tbe 
rate and the time, we bave the thickness. 

One of these three, namely, the rate, can, however, be deter- 
mined with tolerable accuracy if we are simply allowed to 
assume — ^what is very probable, as has already been shown — 
tbat the present rate at which the sedimentary deposits are 
being formed may be taken as the mean rate for past ages. If 
we know the rate at which the land is being denuded, then we 
know with perfect accuracy the rate at which the sedimentary 
deposits are being formed in the ocean. This is obvious, 
because all the materials denuded from the land are deposited in 

♦ • Principles,** vol. i., p. 107. Tenth Edition. 



THICKNESS OF SEDIMENTARY ROCKS. 363 

the sea ; and what is deposited in the sea is just what comes off 
the laud, with the exception of the small proportion of cal- 
careous matter which may not have been derived from the land, 
and which in our rough estimate may be left out of account. 

Now the mean rate of subaerial denudation, we have seen, is 
about one foot in 6,000 years. Taking the proportion of land 
to that of water at 576 to 1,390, then one foot taken off the 
land and spread over the sea-bottom would form a layer 5 
inches thick. Consequently, if one foot in 6,000 years repre- 
sents the mean rate at which the land is being denuded, one 
foot in 14,400 years represents the mean rate at which the 
sedimentary rocks are being formed. 

Assuming, as before, that 72,000 feet would represent the 
mean thickness of all the sedimentary rocks which have ever 
been formed, this, at the rate of one foot in 14,400 years, gives 
1,036,800,000 years as the age of the stratified rocks. 

Professor Huxley, in his endeavour to show that 100,000,000 
years is a period sufSciently long for all the demands of 
geologists, takes the thickness of the stratified rocks at 100,000 
feet, and the rate of deposit at a foot in 1,000 years. One foot 
of rock per 1,000 years gives, it is true, 100,000 feet in 
100,000,000 years. But what about the rocks which havd 
disappeared P If it takes a hundred millions of years to pro- 
duce a mass of rock equal to that which now exists, how many 
hundreds of millions of years will it require to produce a mass 
equal to what has actually been produced P 

Professor Huxley adds, "I do not know that any one is 
prepared to maintain that the stratified rocks may not have 
been formed on the average at the rate of l-83rd of an inch per 
annum." When the rate, however, is accurately determined, 
it is found to be, not l-83rd of an inch per annum, but only 
1.1200th of an inch, so that the 100,000 feet of rock must 
have taken 1,440,000,000 years in its formation, — a conclusion 
which, according to the results of modem physics, is wholly 
inadmissible. 

Either the thickness of the sedimentary rocks has been over- 



|64 .: CLIMATE AND TIME. 

estimated, or the rate of their fonnation has been under* 
estimated, or both. If it be maintained that a foot in 14,400 
years is too slow a rate of deposit, then it must be maintained 
that the land must have been denuded at a greater rate than 
one foot in 6,000 years. But most geologists probably felt 
surprised when the announcement was first made, that i^ this 
rate of denudation the whole existing land of the globe would 
be brought under the ocean in 6,000,000 of years. 

The error, no doubt, consiBts in over-estimating the thibkness 
of the sedimentary rocks. Assuming, for physical reasons 
already stated, that 100,000,000 years limits the age of the 
stratified rocks, and that the proportion of land to water 
and the rate of denudation have been on the average the 
same as at present, the mean thickness of sedimentary rocks 
formed in the 100,000,000 years amounts to only 7,000 feet. 

But be it observed that this is the mean thickness on an area 
equal to that of the ocean. Over the area of the globe it 
amounts to only 5,000 feet ; and this, let it be observed also, is 
the total mean thickness formed, without taking into accoimt 
what has been removed by denudation. If we wish to ascertain 
what is actually the present mean thickness, we must deduct 
from this 5,000 feet an amount of rock equal to all the sedi- 
mentary rocks which have been denuded during the 100,000,000 
years ; for the 5,000 feet is not the present mean thickness, but 
the total mean thickness formed during the whole of the 
100,000,000 years. If we assume, what no doubt most geolo- 
gists would be willing to grant, that the quantity of sedimentary 
rocks now remaining is not over one-half of what has been 
actually deposited during the history of the globe, then the 
actual mean thickness of the stratified rocks of the globe is not 
over 2,500 feet. This startling result would almost necessitate 
us to suspect that the rate of subaerial denudation is probably 
greater than one foot in 6,000 years. But, be this as it may, 
we are apt, in estimating the mean thickness of the stratified 
rocks of the globe from their ascertained maximum thickness, 
to arrive at erroneous conclusions. There are considerations 



THICKNESS OF SEDIMENTARY ROCKS. 365 

which show that the mean thickness of these rocks must be 
small in proportion to their maximum thickness. The stratified 
rocks are formed from the sediment carried down by rivers and 
streamlets and deposited in the sea. It is obvious that the 
greater quantity of this sediment is deposited near the mouths 
of riversy and along a narrow margin extending to no great 
distance from the land. Did the land consist of numerous small 
islands equally distributed over the globe, the sediment carried 
off from these islands would be spread pretty equally over the 
sea-bottom. But the greater part of the land-surface consists 
of two immense continents. Consequently, the materials 
removed by denudation are not spread over the ocean-bottom, 
but on a narrow fringe surroimding those two continents. 
Were the materials spread over the entire ocean-bed, a foot 
removed off the general surface of the land would form a layer 
of rock only five inches thick. But in the way in which the 
materials are at present deposited, the foot removed from the 
land would form a layer of rock many feet in thickness. The 
greater part of the sediment is deposited within a few miles 
of the shore. 

The entire coast-line of the globe is about 116,500 miles. I 
should think that the quantity of sediment deposited beyond, 
say, 100 miles from this coast-line is not very great. No 
doubt several of the large rivers carry sediment to a much 
greater distance from their mouths than 100 miles, and ocean 
currents may in some cases carry mud and other materials also 
to great distances. But it must be borne in mind that at many 
places within the 100 miles of this immense coast-line little 
or no sediment is deposited, so that the actual area over which 
the sediment carried off the land is deposited is probably not 
greater than the area of this belt — 116,500 miles long and 100 
miles broad. This area on which the sediment is deposited, on 
the above supposition, is therefore equal to about 11,650,000 
square miles. The amount of land on the globe is about 
67,600,000 square miles. Consequently, one foot of rock, 
denuded from the surface of the land and deposited on this 



S66 CLIMATE AND TIME. 

belt, would make a stratum of rook 6 feet in thickneet; but 
were the sediment spread over the entire bed of the ooeaii^ it 
would form, as has already been stated, a stratum of rook of 
only 5 inches in thickness. 

Suppose that no subsidence of the land should take plaoe bx 
a period of, say, 3,000,000 of years. During that period 600 
feet would be removed by denudation, on an average, off the 
land. This would make a formation 2,500 feet thick, which 
some future geologist might call the Post-tertiary formation. 
But this, be it observed, would be only the mean thickneai of 
the formation on this area; its maicimum thickness would 
evidently be much greater, perhaps twice, thrice, or even fimr 
times that thickness. A geologist in the future, measuring the 
actual thickness of the formation, might find it in some places 
10,000 feet in thickness, or perhaps far more. But had the 
materials been spread over the entire ocean-bed, the formation 
would have a mean thickness of little more than 200 feet ; and 
spread over the entire surface of tlie globe, would form a 
stratimi of scarcely 150 feet in thickness. Therefore, in 
estimating the mean thickness of the stratified rocks of the 
globe, a formation with a maximimi thickness of 10,000 feet 
may not represent more than 150 feet. A formation with a 
mean thickness of 10,000 feet represents only 600 feet. 

It may be objected that in taking the present rate at which 
the sedimentary deposits are being formed as the mean rate for 
all ages, we probably under-estimate the total amount of rock 
formed, because during the many glacial periods which must 
have occurred in past ages the amount of materials groimd off , 
the rocky surface of the land in a given period would be fiir 
greater than at present. But, in reply, it must be remembered 
that although the destruction in ice-covered regions would be 
greater during these periods than at present, yet the quantity 
of materials carried down by rivers into the sea would be less. 
At the present day the greater part of the materials carried 
down by our rivers is not what is being removed oflf the rocky 
fisce of the country, but the boulder clay, sand, and oth(a* 



THICKNESS OF SEDIMENTARY ROCKS. 367 

materials which were ground off during the glacial epoch. It 
is therefore possible, on this account, that the rate of deposit 
may have been less during the glacial epoch than at present. 

When any particular formation is wanting in a given area, 
the inference generally drawn is, that either the formation has 
been denuded off the area, or the area was a land-surface 
during the period when that formation was being deposited. 
From the foregoing it will be seen that this inference is not 
legitimate ; for, supposing that the area had been under water, 
the chances that materials should have been deposited on that 
area are far less than are the chances that there should not. 
There are sixteen chances against one that no formation oyer 
existed in the area. 

If the great depressions of the Atlantic, Pacific, and Indian 
Oceans be, for example, as old as the beginning of the 
Laurentian period — and they may be so for anything whict 
geology can show to the contrary — then under these oceans 
little or no stratified rocks may exist. The supposition that 
the great ocean basins are of immense antiquity, and that con- 
sequently only a small proportion of the sedimentary strata 
can possibly occupy the deeper bed of the sea, acquires still 
more probability when we consider the great extent and 
thickness of the Old Red Sandstone, the Permian, and other 
deposits, which, according to Professor Bamsay and ^ther8| 
have been accumulated in vast inland lakes. 



ir 



CHAPTER XXIII. 

rHS PHYSICAL CAUSE OF THE STTBMEROENCE AND EUERGENCOI 
OF THE LAND DURING THE OLACIAL EPOCH. 

Displacement of the Earth's Centre of Gravity by Polar Io»-Oftp^ — Simpis 
Method of estiniating Amount of Displacement^Kote by Sir W. Thomson 
on foregoing: Method. — Difference between Continental loe and a QlacMT.— 
ProbabH) Tniokness of the Antarctic Ice-cap. — Probable Thickness of Gh«en- 
land Ice-sheet. — The Icebergs of the Southern Ocean. — Inadequate Con- 
ceptions regarding the Magnitade of Continental Ice. 

Displacement of tlie EartVa Centre of Oravity by Polar Ice-cap* 
—in, order to represent the question in its most simple ele- 
mentary form, I shall assume an ice-cap of a given thickness 
at the pole and gradually diminishing in thickness towards the 
equator in the simple proportion of the sines of the latitudes, 
where at the equator its thickness of course is zero. Let us 
assimie, what is actually the case, that the equatorial diameter 
of the globe is somewhat greater than the polar, but that when 
the ice-cap is placed on one hemisphere the whole forms a 
perfect sphere. 

I shall begin with a period of glaciation on the southern 
hemisphere. Let W N E S' (Fig. 5) be the solid part of the 
earth, and c its centre of gravity. And let E S W be an ice- 
cap covering the southern hemisphere. Let us in the first 
case assume the earth to be of the same density as the cap. 
The earth with its cap forms now a perfect sphere with its 

• The conception of submergence resulting from displacement of the earth's 
centre of gravity, caused by n heaping* up of ice at one of ihe poles, was first 
advanced by M. Adhcmar, in his woii. *" Jitvoiutions dt la Mer^' 1842. When 
the views stated in this cliapter appeared in the Jieadcr, I was not aware that 
M. Adhcmar hud wntt« n ou the subjtK.'t. An accourit of his mode of viewing 
Uie question is given in the Appondix. 



GLACIAL SUBMERGENCE. 



3b9 



centre of gravity at o; for W N E S is a circle, and o is its 
centre. Suppose now the whole to be covered with an ocean 
a few miles deep, the ocean will assume the spherical form, 
and will be of uniform depth. Let the southern winter solstice 
begin now to move round from the aphelion. The ice-cap 
will also commence gradually to diminish in thickness, and 
another cap will begin to make its appearance on the northern 
hemisphere. As the northern cap may be supposed, for sim- 
plicity of calculation, to increase at the same rate that the 
southern will diminish, the spherical form of the earth will 




always be maintained. By the time that the northern cap 
has reached a maximum, the southern cap will have completely 
disappeared. The circle W N' E S' will now represent the 
earth with its cap on the northern hemisphere, and o' will be 
its centre of gravity ; for o* is the centre of the circle W N'E S'. 
And as the distance between the centres o and d is equal to 
N N', the thickness of the cap at the pole N N' will therefore 
represent the extent to which the centre of gravity has been 
displaced. It will also represent the extent to which the ocean 
has risen at the north pole and sunk at the south. This is 
evident ; for as the sphere W N' E S' is the same in all 
respects as the sphere W N E S, with the exception only that 
the cap is on the opposite side, the surface of the ocean at the 
poles will now be at the same distance from the centre d as it 



370 



CLIMATE AND TIME. 



was from the centre o when the cap covered the aouthem head- 
sphere. Hence the distance between o and J must be equal to 
^e extent of the snbmergence at the north pole and the 
emergence at the south. Neglect the attraction of the altering 
water on the water itself, which later on will come under our 
eonsideration. 

We shall now consider the result when the earth is taken at 
its actual density, which is generally believed to be about 5*6. 
The density of ice being *92, the density of the cap to that of 
the earth will therefore be as 1 to 6. 

Kg.s. 




Let Fig. 6 represent the earth with an ice-cap on the 
northern hemisphere, whose thickness is, say, 6,000 feet at the 
pole. The centre of gravity of the earth without the cap is at 
c. When the cap is on, the centre of gravity is shifted to o, a 
point a little more than 500 feet to the north of e. Had the cap 
and the earth been of equal density, the centre of gravity 
would have been shifted to d the centre of the figure, a point 
situated, of l^ourse, 3,000 feet to the north of c. Now it is very 
approximately true that the ocean will tend to adjust itself as 
a sphere around the centre of gravity, o. Thus it would of 
course sink at the south pole and rise to the same extent at the 
north, in any opening or channel in the ice allowing the water 
to enter. 

JiCt the ice-cap be now transferred over to the soathem 



GLACIAL SUBMERGENCE. y^x 

hemispliere, and the condition of tliingB on the two hemi- 
spheres will in every particular be reversed. The centre of 
gravity will then lie to the south of e^ or about 1,000 feet from 
its former position. Consequently the transferrence of the cap 
from the one hemisphere to the other will produce a total 
submergence of about 1,000 feet. 

It is, of course, absurd to suppose that an ice-cap could ever 
actually reach down to the equator. It is probable that the 
great ice-cap of the glacial epoch nowhere reached even half- 
way to the equator. Our cap must therefore terminate at a 
moderately high latitude. Let it terminate somewhere about 
the latitude of the north of England, say at latitude 55^. All that 
we have to do now is simply to imagine our cap, up to that 
latitude, becoming converted into the fluid, state. This would 
reduce the cap to less than one-half its former mass. But it 
would not diminish the submergence to anything like that 
extent. For although the cap would be reduced to less than 
one-half its former mass, yet its influence in displacing the 
centre of gravity would not be diminished to that extent. 
This is evident ; for the cap now extending down to only 
latitude 55°, has its centre of gravity much farther removed 
from the earth's centre of gravity than it had when it extended 
down to the equator. Consequently it now possesses, in pro- 
portion to its mass, a much greater power in displacing the 
earth's centre of gravity. 

There is another fact which must be taken into account. The 
common centre of gravity of the earth and cap is not exactly the 
point around which the ocean tends to adjust itself. It adjusts 
itself not in relation to the centre of gravity of the solid mass 
alone, but in relation to the common centre of gravity of the 
entire mass, solid and liquid. Now the water which is pulled over 
from the one hemisphere to the other by the attraction of the 
cap will also aid in displacing the centre of gravity. It will 
co-operate with the cap and carry the true centre of gravity 
to a point beyond that of the centre of gravity of the earth 
and cap, and thus increase the effect. 



37S CLIMATE AND TIME. 

It is of course perfectly true tbat when the ice«cap dues nol 
extend down to the equator, as in the latter supposition, and is 
of less density than tho globe, the ocean will not adjust itsslf 
unifonnly around the centre of gravity; but the devistian 
from perifect uniformity is so trifling, as will be seen from the 
appended note of Sir William Thomson, that for all practical 
purposes it may be entirely left out of account. 

In the Reader for January 13, 1866, I advanced an ob- 
jection to the submergence theory on the grounds that the 
lowering of the ocean-level by the evaporation of the water to 
form the ice-cap, would exceed the submergence resulting from 
the displacement of the earth's centre of gravity. But» after 
my letter had gone to press, I found that I had overlooked 
some important considerations which seem to prove that the 
objection had no real foimdation. For during a glacial period, 
say on the northern hemisphere, the entire mass of ice which 
presently exists on the southern hemisphere would be trans- 
ferred to the northern, leaviDg the quantity of liquid water to 
a great extent unchanged. 

Note on the preceding hy Sir Willimn Thomson^ F.R.8. 

"Mr. Croll's estimate of the influence of a cap of ice on 
the sea-level is very remarkable in its relation to Laplace's 
celebrated analysis, as being founded on that law of thickness 
which leads to expressions involving only the first term of 
the series of ' Laplace's functions,' or * spherical harmonics.' 
The equation of the level surface, as altered by any given 
transferrence of solid matter, is expressed by equating the 
altered potential function to a constant. This function, when 
expanded in the series of spherical harmonics, has for its first 
term the potential due to the whole mass supposed collected 
at its altered centre of gravity. Hence a spherical surfeuse 
round the altered centre of gravity is the first approximation in 
Laplace's method of solution for the altered level Burffiu^e. 
Mr. Croll has with admirable tact chosen, of all the arbitrary 
suppositions that may be made foundations for rough estimates 



GLACIAL SUBMERGENCE. 373 

of the change of sea-level due to yariations in the polar ice- 
crusts, the one which reduces to zero all terms after the first 
in the harmonic series, and renders that first approximation 
(which always expresses the e%%ence of the result) the whole 
solution, undisturbed by terms irrelevant to the great physical 
question. 

**31r. CrolI,in the preceding paper, has alluded with remark- 
able clearness to the effect of the change in the distribution of 
the water in increasing, by its own attraction, the deviation of 
the level surface above that which is due to the given change in 
the distribution of solid matter. The remark he makes, that 
it is round the centre of gravity of the altered solid and altored 
liquid that the altering liquid surface adjusts itself, expresses 
the essence of Laplace's celebrated demonstration of the stability 
of the ocean, and suggests the proper elementary solution of the 
problem to find the true alteration of sea-level produced by a 
given alteration of the solid. As an assumption leading to a 
simple calculation, let us suppose the solid earth to rise out of 
the water in a vast number of small flat-topped islands, each 
bounded by a perpendicular cliffy and let the proportion of 
water area to the whole be equal in all quarters. Let all of 
these islands in one hemisphere be covered with ice, of thick- 
ness according to the law assumed by Mr. Croll — that is, 
varying in simple proportion of the sine of the latitude. Let 
this ice be removed from the first hemisphere and similarly 
distributed over the islands of the second. By working out 
according to Mr. CroU's directions, it is easily found that the 
change of sea-level which this will produce will consist in a 
sinking in the first hemisphere and rising in the second, 
through heights varying according to the same law (that is, 
simple proportionality to sines of latitudes), and amounting at 

each pole to 

(i--«)f7 

1 — wu; ' 

where t denotes the thickness of the ice-crust at the pole ; • the 
ratio of the density of ice, and w that of sea- water to the earth's 



374 CLIMATE AND TIME. 

mean density ; and m the ratio of the aiea of ocean to tk 
whole Bur&ce. 

** Thus, for instance, if we suppose « = f, and t = 6,000 feet| 

11 
and take ^ and j. as the densities of ice and water respectiTdjf 

we find for the rise of sea-level at one pole, and depreanon at 
the other, 

i X i X 6000 

— i i ' 

3 h\ 

or approximately 380 feet. 

I shall now proceed to consider roughly what is the probable 
extent of submergence which, during the glacial epoch, may 
haye resulted from the displacement of the earth's centre ol 
gravity by means of the transf errenee of the polar ice from the 
one hemisphere to the other. 

Difference between ContinentaUice and a Glacier, — ^An ordinary 
glacier descends in virtue of the slope of its bed, and, as a 
general rule, it is on this account thin at its commencement^ 
and thickens as it descends into the lower valleys, where the 
slope is less and the resistance to motion greater. But in the 
case of continental ice matters are entirely different. The 
slope of the ground exercises little or no influence on the mo- 
tion of the ice. In a continent of one or two thousand miles 
across, the general slope of the ground may be left out of 
account ; for any slight elevation which the centre of such a 
continent may have will not compensate for the resistance 
offered to the flow of the ice by mountain ridges, hills, and other 
irregularities of its surface. The ice can move off such a sur- 
face only in consequence of pressure acting from the interior. 
In order to produce such a pressure, there must be a piling up 
of the ice in the interior ; or, in other words, the ice-sheet 
must thicken from the edge inwards to the centre. We are 
necessarily led to the same conclusion, though we should not 
admit that the ice moves in consequence of pressure from 
behind, but should hold, on the contrary, that each particle of 



GLACIAL SUBMERGENCE. 17$ 

ice moveB by gravity in virtue of its own weight ; for in order 
to have such a motion there must be a slope, and as the slope ia 
not on the ground, it must be on the ice itself: conse- 
quently we must conclude that the upper surface of the ice 
slopes upwards from the edge to the interior. What, then, is 
the least slope at which the ice will descend P Mr. Hopkias 
found that ice barely moves on a slope of one degree. We have 
therefore some data for arriving at least at a rough estimate of 
the probable thickness of an ice-sheet covering a continent, 
such, for example, as Greenland or the Antarctic Continent. 

Probable Thickness of the Antarctic Ice-cap, — The antarctic 
continent is generally believed to extend, on an average, from 
the South Pole down to about, at least, lat. 70^. In round num- 
bers, we may take the diameter of this continent at 2,800 miles* 
The distance from the edge of this ice-cap to its centre, the 
South Pole, will, therefore, be 1,400 miles. The whole of this 
continent, like Greenland, is imdoubtedly covered with one 
continuous sheet of ice gradually thickening inwards from its 
edge to its centre. A slope of one degree continued for 1,400 
miles will give twenty-four miles as the thickness of the ice at 
the pole. But suppose the slope of the upper surface of the 
cap to be only one-half this amount, viz., a half degree, — and 
we have no evidence that a slope so small would be sufficient to 
discharge the ice, — still we have twelve miles as the thickness 
of the cap at the pole. To those who have not been accus- 
tomed to reflect on the physical conditions of the problem, this 
estimate may doubtless be regarded as somewhat extravagant ; 
but a slight consideration will show that it would be even more 
extravagant to assume that a slope of less than half a degree 
would be sufficient to produce the necessary outflow of the ice. 
In estimating the thickness of a sheet of continental ice of one 
or two thousand miles across, our imagination is apt to deceive 
us. We can easily form a pretty accurate sensuous representa- 
tion of the thickness of the sheet ; but we can form no adequate 
representation of its superficial area. We can represent to the 
mind with tolerable accuracy a thickness of a few miles, but we 



S7« 



CLIMATE AND TIME. 




oannot do tliis in reference to the area of a snrfiice 2,800 mi 
across. Consequently, in judging what proportion the fhic 
ness of the sheet should h^ to its superficial area, we are i 
to fall into the error of under-estiniating the thickness. 1 
have a striking example of this in regard to the ocean. 1 
thing which impresses us most forcibly in r^;ard to the ooc 
is its profoimd depth. A mean depth of, say, three miles p 
duces a striking impression ; but if we could represent to 1 
mind the yast area of the ocean as correctly as we can do 
depth, shallowness rather than depth would be the impread 
produced. A sheet of water 100 yards in diameter, and on 
one inch deep, would not be called a deep but a yery shoD 
pool or thin layer of water. But such a layer would be a C4 
rect representation of the ocean in miniature. Were we 
like manner to represent to the eye in miniature the antarc 
ice-cap, wo would call it a thin crust of ice. Taking the me 
thickness of the ice at four miles, the antarctic ice-sheet wov 
be represented by a carpet covering the floor of an ordinal 
sized dining-room. "Were those who consider the above es 
mate of the thickness of the antarctic ice-cnp as extravagant 
great called upon to sketch on paper a section of what th 
should deem a cap of moderate thickness, ninety-nine out 
every hundred would draw one of much greater thickness thi 
twelve miles at the centre. 

The diagram on following page (Fig. 7) represents a secti 
across the cap drawn to a natural scale ; the upper sur£Eice 
the sheet having a slope of half a degree. No one on lookii 
at the section would pronounce it to be too thick at the cent: 
unless he were previously made aware that it represented 
thickness of twelve miles at that place. It may be here me 
iioned that had the section been drawn upon a much larg 
scale — had it, for instance, been made seven feet long, inste 
of seven inches — ^it would have shown to the eye in a mc 
striking manner the thinness of the cap. 

But to avoid all objections on the score of over-estimati] 
the thickness of the cap, I shall assume the angle of the upj 



GLACIAL SUBMERGENCE. 



J77 



fcorface to be only a quarter of a degree, and the 
thickness of the sheet one-half what it is repre- 
sented in the section. The thickness at the pole 
will then be only six miles instead of twelve, 
and the mean thickness of the cap two instead of 
four miles. 

Is there any well-grounded reason for conclud- 
ing the above to be an over-estimate of the actual 
thickness of the antarctic ice P It is not so much 
in consequence of any d, priori reason that can be 
urged against the probability of such a thickness 
of ice, but rather because it so far transcends our 
previous experience that we are reluctant to 
admit such an estimate. If we never had any 
experience of ice thicker than what is found in 
England, we should feel startled on learning for 
the first time that in the valleys of Switzerland 
the ice lay from 200 to 300 feet in depth. 
Again, if we had never heard of glaciers thicker 
than those of Switzerland, we coidd hardly 
credit the statement that in Greenland they are 
actually from 2,000 to 3,000 feet thick. We, 
in this country, have long been familiar with 
Greenland ; but till very lately no one ever enter- 
tained the idea that that continent was buried 
under one continuous mass of ice, with scarcely a 
mountain top rising above the icy mantle. And 
had it not been that the geological phenomena 
of the glacial epoch have for so many years 
accustomed our minds to such an extraordinary 
condition of things, Dr. Rink's description of the 
Greenland ice would probably have been re- 
garded as the extravagant picture of a wild 
imagination. 

Let us now consider whether or not the facts 
of observation and experience, so far as they go. 



i 



o 

to P4 



P^ 



CQ 



8 



c« 



II 



I 

o 

2 
a 

8 



i 

ears 

u 

^ 00 

-.St 

pi 

^^ ^tf " 

Silt 
» S 9 

s _ *•* 
O Hi CQ 



378 CLIMATE AND TIME. 

bear out the conclusions to which physical conflidentions lead 
us in reference to tho magnitude of continental ice ; and more 
especially as regards the ice of the antarctic regions. 

First. In so far as the antarctic ice-sheet is concerned, ob- 
servation and experience to a great extent may be said to be a 
perfect blank. One or two voyagers have seen the outer edge 
of the sheet at a few places, and this is alL In fact, we judge 
of the present condition of the interior of the antarctie oomti.- 
nent in a great measure from what we know of Greenland* 
But again, our experience of Greenland ice is almost wholly 
confined to the outskirts. 

Few have penetrated into the interior, and, with the exception 
of Dr. Hayes and Professor Nordenskjold, none, as £Eir as I kno^, 
have passed to any considerable distance over the inland ice. 
Dr. Eobcrt Brown in his interesting memoir on '' Das Innere von 
Gronland," * gives an account of an excursion made in 1747 by a 
Danish officer of the name of Dolager, from Fredrikshaab, near 
the southern extremity of the continent, into the interior. After 
a journey of a day or two, he reached an eminence from which 
he saw tiie inland ice stretching in an unbroken mass as far as 
the eye could reach, but was unable to proceed further. Dr. 
Brown gives an account also of an excursion made in the 
beginning of March, 1830, by 0. B. Kiclsen, a Danish whale- 
fisher, from Holsteinborg (lat. 67° N.). After a most fatiguing 
journey of several days, he reached a high point from which he 
could see the ice of the interior. Next morning he got up early, 
and towards midday reached an extensive plain. From this 
the land sank inwards, and Kielsen now saw fully in view be- 
fore him the enormous ice-sheet of the interior. He drove 
rapidly over all the little hills, lakes, and streams, till he 
reached a pretty large lake at the edge of the ice-sheet. This 
was the end of his journey, for after vainly attempting to dimb 
up on the ice>sheot, he was compelled to retrace his steps, and 
had a somewhat difficult return. AVlien he arrived at the 
fiord, he found the ice broken up, so that he had to go round 

• Petennann*8 Geog. Mittheiiunffen, 1871, Heft, x., p. 377. 



GLACIAL SUBMERGENCE. 379 

by the land way, by which he reached the depdt on the 9th of 
March. The distance which he traversed in a straight line 
from Holsteinborg into the interior measured eighty English 
miles. 

Dr. Hayes's excursion was made, however, not upon the 
real inland ice, but upon a smaller ice-field connected 
with it ; while Professor Kordenskjold's excursion was made 
at a place too far south to afford an accurate idea of the 
actual condition of the interior of North Greenland, even 
though he had penetrated much farther than he actually did. 
However, the state of things as recorded by Hayes and by 
Nordenskjold affords us a glimpse into the condition of things 
in the interior of the continent. They both foimd by observa- 
tion, what follows as a necessary result from physical consider- 
ations, that the upper surface of the ice plain, under which 
hills and valleys are buried, gradually 9lope% upwards tawarch the 
interior of the continent. Professor Nordenskjold states that 
when at the extreme poiut at which he reached, thirty geo- 
graphical miles from the coast, he had attained an elevutioti 
of 2,200 feet, and that the inland ice continued constantly to rvue 
towards the interior, so that the horizon towards the east, north, 
and south, was terminated by an ice-border almost as smooth 
as that of the ocean.*'* 

Dr. Hayes and his party penetrated inwards to the distance 
of about seventy miles. On the first day they reached the foot 
of the great Mer de Glace ; the second day's journey carried 
them to the upper surfiice of the ice-sheet. On the third day 
they travelled 30 miles, and the ascent, which had been about 
6°, diminished gradually to about 2°. They advanced on the 
fourth day about 25 miles ; the temperature being 30° below 
zero (Fah.). "Our station at the camp," he says, "was sub- 
lime as it was dangerous. We had attained an altitude of 
6,000 feet above the sea-level, and were 70 miles from the 
coast, in the midst of a vast frozen Sahara immeasurable to 
the human eye. There was neither hill, mountain, nor gorge, 

• Oeol. Mag., 1872, vol. ix , p. 360. 



j8o CLIMATE AND TIME. 

Bnywhere in Tiew. We had completely sunk the strip of land 
between the Mer de Glace and the sea, and no object met the 
eye but our feeble tent, which bent to the storm. Fitful okmds 
swept oyer the face of the full-orbed moon, which, descending 
towards the horizon, glimmered through the drifting snow 
that scudded oyer the icy plain — ^to the eye in undulating lines 
of downy softness, to the flesh in showers of piercing darts.*' * 

Dr. Rink, referring to the inland ice, says that the eleya^ 
lion or height aboye the sea of this icy plain at its junction 
with the outskirts of the country, and where it begins to lower 
itself through the yalleys to the friths, is, in the ramifications 
of the Bay of Omenak, found to be 2,000 feet, from which leyel 
it gradually rises towards the interior, f 

Dr. Robert Brown, who, along with Mr. Whymper in 1867, 
attempted a journey to some distance over the inland ice, is of 
opinion that Greenland is not traversed by any ranges of moun- 
tains or high land, but that the entire continent, 1,200 miles 
in length and 400 miles in breadth, is covered with one con- 
tinuous unbroken field of ice, the upper surface of which, he 
says, rises by a gentle slope towards the interior,t 

Suppose now the point reached by Hayes to be within 200 
miles of the centre of dispersion of the ice, and the mean slope 
from that point to the centre, as in the case of the antarctic 
cap, to be only half a degree ; this would give 10,000 feet as 
the elevation of the centre above the point reached. But the 
point reached was 5,000 feet above sea-level, consequently the 
surface of the ice at the centre of dispersion would be 15,000 
feet above sea-level, which is about one-fourth what I have 
concluded to be the elevation of the surface of the antarctic 
ice-cap at its centre. And supposing we assume the general 
surface of the ground to have in the central region an eleva- 
tion as great as 5,000 feet, which is not at all probable, still this 
would give 10,000 feet for the thickness of the ice at the centrA 

• *« Open PolHr Sea," p. 134. 

f Joomul of the Royal Gerjgraphical Society, 1853, vol. xxiii. 

X *' I'hysicB of Arctic Ice," Quart. Joum. Geol. fcloc. for February, 1871. 



GLACIAL SUBMERGENCE. i%\ 

of the Greenland continent. But if we admit this conclusion 
in reference to the thickness of the Greenland ice, we must 
admit that the antarctic ice is far thicker, because the thick- 
ness, other things being equal, will depend upon the size, or, 
more properlj, upon the diameter of the continent; for the 
larger the surface the greater is the thickness of ice required to 
produce the pressure requisite to make the rate of discharge of 
the ice equal to the rate of increase. Now the area of the 
antarctic continent must be at least a dozen of times greater 
than that of Greenland. 

Second, That the antarctic ice must be far thicker than the 
arctic is further evident from the dimensions of the icebergs 
which have been met with in the Southern Ocean. No ice- 
bergs over three hundred feet in height have been found in the 
arctic regions, whereas in the antarctic regions, as we shall 
see, icebergs of twice and even thrice that height have been 
reported. 

Third, AVe have no reason to believe that the thickness of 
the ice at present covering the antarctic continent is less than 
that which covered a continent of a similar area in temperate 
regions during the glacial epoch. Take, for example, the 
North American continent, or, more properly, that portion of 
it covered by ice during the glacial epoch. Professor Dana 
has proved that during that period the thickness of the ice on 
the American continent must in many places have been con- 
siderably over a mile. He has shown that over the northern 
border of New England the ice had a mean thickness of 6,500 
feet, while its mean thickness over the Canada watershed, 
between St. Lawrence and Hudson's Bay, was not less than 
12,000 feet, or upwards of two miles and a quarter (see American 
Journal of Science and Art for March, 1873). 

Fourth, Some may object to the foregoing estimate of the 
amount of ice on the antarctic continent, on the grounds that 
the quantity of snowfall in that region cannot be much. But 
it must be borne in mind that, no matter however small the 
annual amount of snowfall may be, if more falls than is melted^ 



|8i CLIMATE AND TIME. 

the ioe must coutinae to acoumulate year by year till its thiok* 
BBSS in the centre of the continent be sufficiently great to pro- 
duce motion. The opinion that the snow&U of the antajpotio 
regions is not great does not, howeyer, appear to be borne tmft 
by the observation and ezperience of those who have vioited 
those regions. Captain Wilkes, of the American Eicploring 
Expedition, estimated it at 30 feet per annum ; and Sir James 
Boss says, that during a whole month they had only three daya 
free from snow. The fact that perpetual snow is found at tiia 
sea-level at kt. 64^ S. proves that the snowMl must be great. 
But there is another circumstance which must be taken into 
account, viz., that the currents carrying moisture move in from 
all directions towards the pole, consequently the area on whidi 
they deposit their snow becomes less and less as the pole is 
reached, and this must, to a corresponding extent, increase the 
quantity of snow failing on a given area. Let us assume, for 
example, that the clouds in passing from lat. 60^ to lat. 80^ 
deposit moisture sufficient to produce, say, 30 feet of snow per 
annum, and that by the time they reach lat. 80^ they ace in 
possession of only one-tenth part of their original store of mois- 
ture. As the area between lat. 80^ and the pole is but one- 
eighth of that between lat. 60° and 80°, this would, notwith- 
standing, give 24 feet as the annual amount of snowfall between 
lat. 80° and the pole.* 

Fifth, The enormous size and thickness of the icebergs which 
have been met with in the Southern Ocean testify to the thick- 
ness of the antarctic ice-cap. 

We know from the size of some of the icebergs which have 
been met with in the southern hemisphere that the ice at the 
edge of the cap where the bergs break off must in some cases 
be considerably over a mile in thickness, for icebergs of more 

• Some writers have objected to the conclasion that the antarctic ice-cap is 
thickest at the pole, on the ground that the snowfall there is probably less than 
at lower latitudes. The fact is, however, overlooked, that the greater thickness 
of an ice-cap at its centre is a physical nece6sity not depending on the rate of 
snowfall. Supposing the snowfall to be greater at, sny, lat. 70^ than at 80**, and 
greater at 80° than at the pole ; nevertheless, the ice will continue to accvmulat* 
till it is thicker at 80" th in at 70% and at the pole than it is at 80^ 



GLACIAL SUBMERGENCE. 383 

dian a mile in thickness have been found in the southern hemi- 
sphere. The following are the dimensions of a few of these 
enormous bergs taken &om the Twelfth Number of the 
Meteorological Papers published by the Board of Trade, and 
from the excellent paper of Mr. Towson on the Icebergs of the 
Southern Ocean, published also by the Board of Trade.* With 
one or two exceptions, the heights of the bergs were accurately 
determined by angular measurement : — 
Sept. 10th, 1856.— The Lightning, when in lat. 65° 33' S., 

long. 140° W., met with an iceberg 420 feet high. 
Nov., 1839. — In lat. 41° S., long. 87° 30' E., numerous icebergs 

400 feet high were met with. 
Sept., 1840. — In lat. 37° S., long. 15° E., an iceberg 1,000 feet 

long and 400 feet high was met with. 
Feb., 1860. — Captain Clark, of the Lightning^ when in lat. 
65° 20' S., long. 122° 45' W., found an iceberg 500 feet 
high and 3 miles long. 
Dec. 1st, 1859. — ^An iceberg, 580 feet high, and from two 
and a half to three miles long, was seen by Captain 
Srnithers, of the Edmond, in lat. 60° 52' S., long. 43° 58' 
W. So strongly did this iceberg resemble land, that 
Captain Smithers belieyed it to be an island, and reported 
it as such, but there is little or no doubt that it was in 
reality an iceberg. There were pieces of drift-ice under 
its lee. 
Nov., 1856. — Three large icebergs, 500 feet high, were found 

in lat. 41° 0' S., long. 42° 0' E. 
Jan., 1861. — Five icebergs, one 500 feet high, were met with 

in lat. 55° 46' S., long. 155° 56' W. 
Jan., 1861.— In lat. 66° 10' S., long. 160° 0' W., an iceberg 

500 feet high and half a mile long was found. 
Jan., 1867. — The barque Scout, from the West Coast of 



* It is a pity that at present no record is kept, either by the Board of Trade 
or by the Admiralty, of remarkable iceberg^ which may m>m time to time be 
met with. Such a record might be of little importance to narigation, bat it 
woold certainly be of great service to science. 



iS4 CLIMATE AND TIME. 

Amerioa, on her way to Liyerpool, passed some iceberg* 

600 feet in height, and of great length. 
A.prily 1864. — The tioyal Standard came in collision with an 

iceberg 600 feet in height. 
Dec., 1856. — Four large icebergs, one of them 700 feet bigh, 

and another 500 feet, were met with in lat. 60^ 14' &, 

long. 42° 54' E. 
Dec. 25th, 1861. — ^The Queen of Nations fell in with an icebezg 

in lat. 53° 45' S., long. 170° 0' W., 720 feet high. 
Dec., 1856. — Captain P. Wakem, ship Elkn Radford, found, in 

lat. 52° 31' S., long. 43° 43' W., two large icebergs, one 

at least 800 feet high. 

Mr. Towson states that one of our most celebrated and 

talented naval surveyors informed him that he had seen 

icebergs in the southern regions 800 feet high. 
March 23rd, 1855. — The Agneta passed an iceberg in lat. 

53° 14' S., long. 14° 41' E., 960 feet in height. 
Aug. 16th, 1840. — The Dutch ship, General Baron von Oeen, 

passed an iceberg 1,000 feet high in lat. 37° 32' S., long. 

14° 10' E. 
May 15th, 1859. — The Boseicorth found in lat. 53° 40' S., long 

123° 17' W., an iceberg as large as *' Tristan d'Acunha.'* 
In the regions where most of these icebergs were met with, 
the mean density of the sea is about 1*0256. The density of 
ice is •92. The density of icebergs to that of the sea is there- 
fore as 1 to 1'115 ; consequently every foot of ice above water 
indicates 8*7 feet below water. It therefore follows that those 
icebergs 400 feet high had 3,480 feet under water, — 3,880 feet 
would consequently be the total thickness of the ice. The ice- 
bergs which were 600 feet high would be 4,850 feet thick, thoee 
600 feet high would have a total thickness of 5,820 feet, and 
those 700 feet high would be no less than 6,790 feet thick, 
which is more than a mile and a quarter. The iceberg 960 feet 
high, sighted by the Agneta, would be actually 9,312 feet thick, 
which is upwards of a mile and three-quarters. 

Althoogh the mass of an iceberg below water compared to 



GLACIAL SUBMERGENCE. i%i 

that above may be taken to be about 8*7 to 1, yet it would not 
be always safe to conclude tbat tbe thickness of the ice bel(»w 
water bears the same proportion to its height above. If the 
berg, for eicample, be much broader at its base than at its top^ 
the thickness of the ice below water would bear a less propor- 
tion to the height above water than as 8*7 to 1. But a berg 
such as that recorded by Captain Clark, 500 feet high and 
three miles long, must have had only 1-8*7 of its total thickness 
above water. The same remark applies also to the one seen by 
Captain Smithers, which w<'is 580 feet high, and so large that 
it was taken for an island. This berg must have been 5,628 feet 
in thickness. The enormous berg which came in collision with 
the Royal Standard must have been 5,820 feet thick. It is not 
stated what length the icebergs 720, 960, and 1,000 feet high 
respectively were ; but supposing that we make considerable 
allowance for the possibility that the proportionate thicknesa 
of ice below water to that above may have been less than as 
8-7 to 1, still we can hardly avoid the conclusion that the ice- 
bergs were considerably above a mile in thickness. But if 
there are icebergs above a mile in thickness, then there must 
be land-ice somewhere on the southern hemisphere of that 
thickness. In short, the great antarctic ice-cap must in somo 
places be over a mile in thickness at its edge. 

Inadequate Conceptions regarding the Magnitude of Continental 
Ice. — ^Few things have tended more to mislead geologists in 
the interpretation of glacial phenomena than inadequate con- 
ceptions regarding the magnitude of continental ice. Without 
the conception of continental ice the known facts connected with 
glaciation would be perfectly inexplicable. It was only when 
it was found that the accumulated facts refused to be explained 
by any other conception, that belief in the very existence of 
such a thing as continental ice became common. But although 
most geologists now admit the existence of continental ice, yet, 
nevertheless, adequate conceptions of its real magnitude are by 
no means so common. Tear by year, as the outstanding facts 
connected with glaciation accumulate, wo are compelled to 



|86 CLIMATE AND TIME. 

extend our conceptions of the magnitude of land-ice. lUce 
the following as an example. It was found that the transport 
of the Wastdale Crag blocks, the direction of the striae on the 
islands of the Baltic, on Caithness and on the Orkney, Shet- 
land, and Faroe, islands, the boulder clay with broken slhells in 
Caithness, Holdemess, and other places, were inexplicable on 
the theory of land-ice. But it was so only in consequence of 
the inadequacy of our conceptions of the magnitude of the ice ; 
for a slight extension of our ideas of its thickness has explained 
not only these phenomena,* but others of an equally remark- 
able character, such as the striation of the Long Island and the 
submerged rock-basins around our coasts described by Mr. Jamea 
Geikie. In like manner, if we admit the theory of the gladui] 
epoch propoimded in former chapters, all that is really neces- 
sary to account for the submergence of the land is a slight 
extension of our hitherto pre-conceived estimate of the thick- 
ness of the ice on the antarctic continent. If we simply admit 
a conclusion to which all physical considerations, as we have 
seen, necessarily lead us, viz., that the antarctic continent is 
covered with a mantle of ice at least two miles in thickness, we 
have then a complete explanation of the cause of the submer- 
gence of the land during the glacial epoch. 

Although of no great importance to the question under con 
sideration, it may be remarked that, except during the severest 
part of the glacial epoch, we have no reason to believe that the 
total quantity of ice on the globe was much greater than at pre- 
sent, only it would then be all on one hemisphere. Kemove 
two miles of ice from the antarctic continent, and place it on the 
northern hemisphere, and this, along with the ice that now 
exists on this hemisphere, would equal, in all probability, the 
quantity existing on our hemisphere during the glacial epoch ; 
at least, before it reached its maximum severity. 

^ See Chapter XXYII., and also Geol. Mag. for May and Jime, 1S70, and 
January, 1871. 



CHAPTER XXIV. 

THE PHYSICAL CAUSE OF THE SUBMBBOENCE AND EBCERGENCB Of 
THE LAND DURING THE GLACIAL EPOCH. Continued. 

Extent of Submergence from Displacement of Earth's Centre of Gravity. — 
Circumstances which show that the Glacia^ Submergence resulted nrom 
Displacement of the Earth's Centre of G^vity. — ^Agreement between Theory 
and observed Facts. — Sir Charles Lyell on submerged Areas during Tertiary 
Period. — Oscillations of Sea-level in Relation to Distribution.— -Extent of 
Submergence on the Hyx>othesis that the Earth is fluid in the Interior. 

Extent of Submergence from Displacement of JEarth*8 Centre 
of Gravity, — How much, then, would the transference of the 
two miles of ice from the southern to the northern hemisphere 
raise the level of the ocean on the latter hemisphere P This 
mass, be it observed, is equal to only one-half that represented 
in our section. A considerable amount of discussion has arisen 
in regard to the method of determining this point. According 
to the method already detailed, which supposes the rise at the 
pole to be equal to the extent of the displacement of the earth's 
centre of gravity, the rise at the North Pole would be about 
380 feet, taking into account the effect produced by the dis- 
placed water ; and the rise in the latitude of Edinburgh would 
be 132 feet. The fall of level on the southern hemisphere 
would, of course, be equal to the rise of level on the northern. 
According to the method advanced by Mr. D. D. Heath,* the 
rise of level at the North Pole would be about 660 feet. Arch- 
deacon Pratt's method t makes the rise stiU greater ; while 
according to Rev. 0. Fisher's method^ the rise would be no 

• Phil. Mag. for April, 18C6, p. 323. 
t Ibid., for March, 1866, p. 172. 
X lUader, February 10, 1866. 



388 CUM ATE AND TIME. 

less than 2,000 feet There is, however, another oircanigtmeo 
which must be taken into account, which will give an addi- 
tional rise of upwards of one hundred feet. 

The greatest extent of the displacement of the eardi's centre 
of- gravity, and consequently the greatest rise of the ocean 
resulting from that displacement, would of course occur at the 
time of maximum gladation, when the ice was all on one 
hemisphere. But owing to the following circumstance, a still 
greater rise than that resulting from the displacement of the 
earth's centre of gravity alone might take place at some eoi^ 
siderable time, either before or after the period of TniLTiimim 
glaciation. 

It is not at all probable that the ice would melt on the warm 
hemisphere at exactly the same rate as it would form on the 
cold hemisphere. It is probable that the ice would melt more 
rapidly ou the warm hemisphere than it would form on the 
cold. Suppose that during the glacial epoch, at a time wlien 
the cold was gradually increasing on the northern and the 
warmth on the southern hemisphere, the ice should melt more 
rapidly off the antarctic continent than it was being formed on 
the arctic and sub-arctic regions; suppose also that, by the 
time a quantity of ice, equal to one-half what exists at present 
on the antarctic coutinent, had accumulated on the northern 
hemisphere, the whole of the antarctic ice had been melted 
away, the sea would then be fuller than at present by the 
amount of water resulting from the one mile of melted ice. 
The height to which this would raise the geneml level of the 
sea would be as follows : — 

The antarctic ice-cap is equal in area to y^ Vir ^^ ^^*^ covered 
by the ocean. The density of ice to that of water being taken 
at "92 to 1, it follows tliat 25 feet 6 inches of ice melted off the 
cap would raise the general level of the ocean one foot, and the 
one mile of ice melted off would raise the level 200 feet This 
200 feet of rise resulting from the melted ice we must add to 
the rise resulting from the displacement of the earth's centre of 
gra\nty. The removal of the two miles of ice from the antarctic 



GLACIAL SUBMERGENCE. 389 

continent would displace the centre of gravity 190 feet^ and 
the formation of a mass of ice equal to the one-half of this on 
the arctic regions would carry the centre of gravity 95 feet 
farther ; giving in all a total displacement of 285 feet, thus 
producing a rise of sea-level at the North Pole of 285 feet, and 
in the latitude of Edinburgh of 234 feet. Add to this the rise 
of 200 feet resulting from the melted ice, and we have then 
485 feet of submergence at the pole, and 434 feet in the latitude 
of Edinburgh. A rise to a similar extent might probably take 
place after the period of maximum glaciation, when the ice 
would be melting on the northern hemisphere more rapidly 
than it would be forming on the southern. 

If we assume the antarctic ice-cap to be as thick as is repre- 
sented in the diagram, the extent of the submergence would of 
course be double the above, and we might have in this case a 
rise of sea-level in the latitude of Edinburgh to the extent of 
from 800 to 1,000 feet. But be this as it may, it is evident 
that the quantity of ice on the antarctic continent is perfectly 
sufficient to account for the submergence of the glacial epoch, 
for we have little evidence to conclude that the general sub- 
mergence much exceeded 400 or 500 feet.* We have evidence 
in England and other places of submergence to the extent of 
from 1,000 to 2,000 feet, but these may be quite local, result- 
ing from subsidence of the land in those particular areas. 
Elevations and depressions of the land have taken place in all 
ages, and no doubt during the glacial epoch also. 

Circurmtancea which show that the Glacial Submergence resulted 
from Displacement of the EartVs Centre of Gravity. — In favour 
of this view of the cause of the submergence of the glacial 
epoch, it is a circumstance of some significance, that in every 
part of the globe where glaciation has been foimd evidence of 
the submergence of the land has also been found along with it. 
The invariable occurrence of submergence along with glaciation 

* In a former paper I considered the eflfects of another cause, viz., the melting 
of polar ice resulting from an increase of ihe Obliquity ot the Earth's Orbit. — 
Trans. Glasi^ow Geol. See., vol. ii., p. 177. Phil. Mag., June, 1867. See also 
Chapter XXV. 



390 CUM ATE AND TIME. 

points to some physical connection between the two. It woaU 
seem to imply^ either that the two were the direct eflbcts of a 
common cause, or that the one was the cause of the other ; thai 
is, the submergence the cause of the glaciation, or the gladai- 
tion the cause of the submergence. There is, I preenme^ no 
known cause to which the two can be directly related as eflEeefts. 
Nor do I think that there is any one who would suppose thai 
the submergence of the land could have been the cause of its 
glaciation, even although he attributed all glacial eflfocti to 
floating ice. The submergence of our country would, of eourae^ 
have allowed floating ice to pass over it had there been any to 
pass over ; but submergence would not have produced the ioe^ 
neither would it have brought the ice from the arctio regions 
where it already existed. But although submergence could 
not have been the cause of the glacial epoch, yet we can, as we 
have just seen, easily understand how the ice of the glacial 
epoch could have been the cause of the submergence. If the 
glacial epoch was brought about by an increase in the eccen- 
tricity of the earth's orbit, then a submergence of the land as 
the ice accumulated was a physical necessity. 

There is another circumstance connected with glacial sub- 
mergence which it is difficult to reconcile with the idea that it 
resulted from a subsidence of the laod. It is well known 
that during the glacial epoch the land was not once under 
water only, but several times ; and, besides, there were not 
merely several periods when the land stood at a lower level in 
relation to the sea than at present, but there were also several 
periods when it stood at a much higher level than now. And 
this holds true, not merely of our own coimtry, but of every 
country on the northern hemisphere where glaciation has yet 
been found. All this follows as a necessary consequence from 
the theory that the oscillations of sea-level resulted from the 
transference of the ice from the one hemisphere to the other ; 
but it is wholly inconsistent with the idea that they resulted 
from upheavals and subsidence of the land during a very recent 
period. 



GLACIAL SUBMERGENCE. 391 

But this is not all, there is more still to be accounted for. It 
has been the prevailing opinion that at the time when the land 
was covered with ice^ it stood at a much greater elevation than 
at present. It is, however, not maintained that the facts of 
geology establish such a conclusion. The greater elevation of 
the land is simply assumed as an hypothesis to account for the 
cold.* The facts of geology, however, are fast establishing the 
opposite conclusion, viz., that when the coimtry was covered 
with ice, the land stood in relation to the sea at a lower level 
than at present, and that the continental periods or times when 
the land stood in relation to the sea at a higher level than now 
were the warm inter-glacial periods, when the country was free 
of snow and ice, and a mild and equable condition of climate 
prevailed. This is the conclusion towards which we are being 
led by the more recent revelations of surface geology, and also 
by certain facts connected with the geographical distribution of 
plants and animals during the glacial epoch. 

The simple occurrence of a rise and fall of the land in relation 
to the sea-level in one or in two countries during the glacial 
epoch, would not necessarily imply any physical connection. 
The coincidence of these movements with the glaciation of the 
land might have been purely accidental ; but when we find that 
a succession of such movements occurred, not merely in one or 
in two countries, but in every glaciated country where proper 
observations have been made, we are forced to the conclusion 
that the connection between the two is not accidental, but the 
result of some fixed cause. 

If we admit that an increase in the eccentricity of the earth's 
orbit was the cause of the glacial epoch, then we must admit 
that all those results followed as necessary consequences. For 
if the glacial epoch lasted for upwards of one hundred thousand 
years or so, there would be a succession of cold and warm 
periods, and consequently a succession of elevations and depres- 
sions of sea-level. And the elevations of the sea-level would 

* Phil. Mag. for November, 1S68, p. 376. 

18 



591 CLIMATE AND TIME. 

take place during the cold periods, and the depresnona durmg 
the wann periods. 

But the agreement between theory and observed &ot8 doet 
not terminate here. It follows from theory that the greatest 
oscillations of sea-level would take place during the eeverest 
part of the glacial epoch, when the eccentricity of the earth's 
orbit would be at its highest value, and that the oscillations 
would gradually diminish in extent as the eccentricity dimi- 
nished and the climate gradually became less severe. Now it 
is well known that this is actually what took place ; the great 
submergence, as well as the great elevation or contineintal 
period, occurred during the earlier or more severe part of the 
glacial epoch, and as the climate grew less severe these changes 
became of less extent, till we find them terminating in our 
submerged forests and 26-foot raised beach. 

It follows, therefore, according to the theory advanced, that 
the mere fact of an area having been under sea does not imply 
that there has been any subsidence or elevation of the land, 
and that consequently the inference which has been drawn 
from these submerged areas as to changes in physical geography 
may be in many cases not well founded. 

Sir Charles Lyell, in his "Principles," publishes a map 
showing the extent of surface in Europe which has been covered 
by the sea since the earlier part of the Tertiary period. This 
map is intended to show the extraordinary amount of subsi* 
dence and elevation of the land which has taken place during 
that period. It is necessary for Sir Charles's theory of the cause 
of the glacial epoch that changes in the physical geography of 
the globe to an enormous extent should have taken place during 
a very recent period, in order to account for the great change 
of climate which occurred at that epoch. But if the foregoing 
results be anything like correct, it Joes not necessarily follow 
that there must have been great changes in the physical geo- 
graphy of Europe, simply because the sea covered those areiis 
marked in the map, for this may have been produced by oscil- 
lations of sea-level, and not by changes in the land. In fact, 



GLACIAL SUBMERGENCE. 393 

the areas marked in Sir Charles's map as haring been covered 
by the sea, are just those which would be covered were the sea- 
level raised a few hundred feet. No doubt there were elevations 
and subsidences in many of the areas marked in the map during 
the Tertiary period, and to this cause a considerable amount of 
the submergence might be due ; but I have little doubt that by 
far the greater part must be attributed to oscillations of sea- 
level. It is no objection that the greater part of the shells and 
other organic remains found in the marine deposits of those 
areas are not indicative of a cold or glacial condition of climate, 
for, as we have seen, the greatest submergence would probably 
have taken place either before the more severe cold had set in 
or after it had to a great extent passed away. That the sub- 
mergence of those areas probably resulted &om elevations of 
sea-level rather than depressions of the land, is further evident 
from the following considerations. If we suppose that the 
climate of the glacial epoch was brought about mainly by 
changes in the physical geography of the globe, we must 
assume that these great changes took place, geologically speak- 
ing, at a very recent date. Then when we ask what ground is 
there for assuming that any such change in the relations of sea 
and land as is required actually took place, the submergence of 
those areas is adduced as the proof. Did it follow as a physical 
necessity that all submergence must be the result of subsidence 
of the land, and not of elevations of the sea, there would be 
some force in the reasons adduced. But such a conclusion by 
no means follows, and, d priori^ it is just as likely that the 
appearance of the ice was the cause of the submergence as that 
the submergence was the cause of the appearance of the ice. 
Again, a subsidence of the land to the extent required would to 
a great extent have altered the configuration of the coiintry, and 
the main river systems of Europe ; but there is no evidence 
that any such change has taken place. All the main valleys 
are well known to have existed prior to the glacial epoch, and 
our rivers to have occupied the same channels then as they do 
now. In the case of some of the smaller streams, it is true, a 



I 



IM CLIMATE AXD TIME. 

aliglit devifttiofi Ihm icsnhed st «■» points £noM the fifficg* i^ 
i£ their ehjmn^h vith drift darizig the giacial epoch; hoi a* a 
gencsal role aU the prxoGpai TiIIeTi and zxvcr sjBt«B^ 
thea the g^adel epodu Thfii^ of eoone, could aoi he the cwb 
if a fohndenee of the land autBr i witlr gtcat to aeeooit finr the 
anbaMrgenee of the areas ia qnestkiii, or changes in the physical 
geogiaphy of Enzope necessazr to produce a glacial epoch, had 
aetnally taken place. The total absence of anr geological evi- 
dence tsx the CTJBtence of anr change which coold explain 
cither the submergence of the areas in question or the climate 
of the glacial epoch, is strong evidenoe that the submergence 
of the glacial epoch, as wdl as of the areas in question, waa the 
result of a simple oscillation of sea-lcTel resulting from the dis- 
placement of the earth's centre of gravity by the transferrenoe 
of the ice-cap from the southern to the northern hemi^phe^e. 

OwillatioM of Sea-krel in relation to Distribution. — ^The 06cilla> 
tions of sea-level resulting from the displacement of the earth's 
centre of gravity help to throw new light on some obscure 
points connected with the subject of the geographical distribu- 
tion of plants and animals. At the time when the ice was on 
the southern hemisphere during the glacial epoch, and the 
northern hemisphere was enjoying a warm and equable climate, 
the sea-level would be several hundred feet lower than at pre- 
sent, the North Sea would probably bo dry land, and Oreat 
Britain and Ireland joined to the continent, thus opening up a 
{Niihway from the continent to our island. As has been shown 
in former chapters, during the inter-glacial periods the climate 
would bo much wanner and more equable than now, so thai 
iinitnulH from the south, such as the hippopotamus, hysenay lion, 
JiirphftH antiquHH and Rhinoceros megarhinua, would migrate into 
ill is country, whcro at prcRcnt they could not live in consequence 
of the cold. Wo have thcreforo an explanation, as was suggested 
o n a fornior oiuumion,* of the fact that the bones of these animals 
11 ro f«nnul mingled in the same grave with those of the musk 
ox, tnannnoih, roindeor, and other animals which lived in this 

• Phil. Maff., November. 18GS. 



GLACIAL SUBMERGENCE. 595 

country during the cold periods of the glacial epoch ; the ani- 
mals from the north would cross over into this country upon 
the frozen sea during the cold periods, while those from the 
south would find the English Channel dry land during the 
warm periods. 

The same reasoning will hold equally true in reference to the 
old and new world. The depth of Behring Straits is under 
30 fathoms ; consequently a lowering of the sea-level of less 
than 200 feet would connect Asia with America, and thus allow 
plants and animals, as Mr. Darwin believes, to pass from the 
one continent to the other.* During this period, when Behring 
Straits would be dry land, Greenland would be comparatively 
free from ice, and the arctic regions enjoying a comparatively 
mild climate. In this case plants and animals belonging to 
temperate regions could avail themselves of this passage^ and 
thus wo can explain how plants belonging to temperate regions 
may have, during the Miocene period, passed from the old to 
the new continent, and tnce versd. 

As has already been noticed, during the time of the greatest 
extension of the ice, the quantity of ice on the southern hemi- 
sphere might be considerably greater than what exists on the 
entire globe at present. In that case there might, in addition 
to the lowering of the sea-level resulting from the displacement 
of the earth's centre of gravity, be a considerable lowering 
resulting from the draining of the ocean to form the additional 
ice. This decrease and increase in the total quantity of ice 
which we have considered would affect the level of the ocean as 
much at the equator as at the poles ; consequently during the 
glacial epoch there might have been at the equator elevations 
and depressions of sea-level to the extent of a few hundred feet. 

Extent of Submergence on the Hypothem that the Earth is fluid 
in the Interior. — But we have been proceeding upon the supposi- 
tion that the earth is solid to its centre. If we assume, how- 
ever, what is the general opinion among geologists, that it 
consists of a fluid interior surrounded by a thick and rigid crust 

• ** Origin of Species,'* chap. xi. Piflh Edition. 



f9» CLIMATE AND TIME. 

or ahell, then the extent of the submergence resulting from ths 
disj^aoemont of the centre of gravity for a given thickiiiati of 
ioe mnst be much greater than I have estimBted it to ba Hoi 
is evident, because, if the interior of the globe be in a fluid 
state, it, in all probability, consists of materials differing in 
density. The densest materials will be at the centre, and the 
least dense at the outside or surikce. Kow the transferrenoo of an 
ice-cap from the one pole to the other vill not merely diaplace 
the ocean — ^the fluid mass on the outside of the shell — but it 
vill also displace the heavier fluid materials in the intoior of 
the shell. In other vrords, the heavier materials will be attracted 
by the ice-cap more forciUy than the lighter, consequently they 
will approach towards the cap to a certain extent, sinking, as it 
were, into tho lighter materials, and displacing them towards 
the opposite pole. This displacement will of course tend to 
shift the earth's centre of gravity in the direction of the ice- 
cap, because the heavier materials are shifted in this direction, 
and the lighter materials in the opposite direction. This proceu 
will perhaps be better understood from the following figures. 
Fig. 8. Fig. 9. 




0, The Ocean. S, Bilirl Crust or ShfU. 
F, F', F', F>. The varioui conceotrio lajen of Uke fluid intaiior. He kjni 

inrntue io deniily lowudi the oenbe. 

1. Th« Ice'Cap. 0. Centre of gr^Tity. 
C. Tbe dilpUced oentre of gimTity 



GLACIAL SUBMERGENCE. 397 

In Fig. 8, where there is no ice- cap, the centre of gravity 
of the earth coincides with the centre of the concentric layers 
of the fluid interior. In Fig. 9, where there is an ice-cap 
placed on one pole, the concentric layer F^ being denser than 
layer F, is attracted towards the cap more forcibly than F, and 
consequently sinks to a certain depth in F. Again, F^ being 
denser than F^ it also sinks to a certain extent in F^ And 
again F^ the mass at the centre, being denser than F^ it also 
sinRs in F*. All this being combined with the effects of the 
ice-cap, and the displaced ocean outside the shell, the centre of 
gravity of the entire globe will no longer be at C, but at C*, a 
considerable distance nearer to the side of the shell on which 
the cap rests than C, and also a considerable distance nearer 
than it would have been had the interior of the globe been 
solid. There are here three causes tending to shift the centre 
of gravity, (1) the ice-cap, (2) the displaced ocean, and (3) the 
displaced materials in the interior. Two of the three causes 
mutually re-act on each other in such a way as to increase each 
other's effect. Thus the more the ocean is drawn in the direc- 
tion of the ice-cap, the more effect it has in drawing the heavier 
materials in the interior in the same direction ; and in turn the 
more the heavier materials in the interior are drawn towards 
the cap, the greater is the displacement of the earth's centre of 
gravity, and of course, as a consequence, the greater is the dis- 
placement of the ocean. It may be observed also that, other 
things being equal, the thinner the solid crust or shell is, and 
the greater the difference in the density of the fluid materials 
in the interior, the greater will be the extent of the displace- 
ment of the ocean, because the greater will be the displacement 
of the centre of gravity. 

It follows that if we knew (1) the extent of the general sub- 
mergence of the glacial epoch, and (2) the present amount of 
ico on the southern hemisphere, we could determine whether or 
not the earth is fluid in the interior. 



CHAPTER XXV. 

THl INFLUEHCB OF THE OBLIQUITY OF THE ECLIFTIC OH GUMAXI 

AND ON THB LBYBL OF THE SEA» 

TIm direct Effect of Chan)^ of Obliquity on Climate.— Hr. Stockwi^ <m ib» 
maziBiiiiii Change of Obliqnity.— -How Obliqaity aifocts the TO atriUuti on of 
Heat OTer the Globe. — ^Increnee of Obliqnitv diminiehee the Heat at Hm 
Equator and increases that at the Poles.— -Influence of Change of Obliqai^ 
on the Level of the Sea. —When the Obh'qaity was last at its superior Lunit. 
—Probable Date of the 25-foot rained Boach. — Probable Extent of Biae of 
Rea-level resulting from Increase of Obliquity. — Lioutenant-Colonel Dray- 
son's aud Mr. Belt's Theories. — Sir Charles Lyell on Influence of Obliquity. 

The direct Effect of Change in the Obliquify of the Ecliptie on 
Climate. — ^There is still another cause which, I feel convinced, 
muBt to a very considerable extent have affected climate during 
past geological ages. I refer to the change in the obliquity of 
tho ecliptic. This cause has long engaged the attention of 
geologists and physicists, and the conclusion generally come to 
is that no great effect can be attributed to it. After giving 
special attention to the matter, I have been led to the very 
opposite conclusion. It is quite true, as has been urged, that 
the changes in the obliquity of tho ecliptic cannot sensibly affect 
the climate of temperate regions ; but it will produce a slight 
change on the climate of tropical latitudes, and a very con- 
siderable effect on that of the polar regions, especially at the 
poles themselves. We shall now consider the matter briefly. 

It was found by Laplace that the obliquity of the ecliptic will 
oscillate to the extent of 1^ 22' 34" on each side of 23° 28*, the 
obliquity in the year 1801.* This point has lately been 

• Lientennnt-Colonel Drayson (*' Lnst Glacial Epoch of Geolo|2y'*) and al'to 
Mr. Belt (Quart. Joum. n( Scieneo, Ot tober, 1874) state that Levemer hae lafe'v 
etigated iho question ns to the extent of the variation of the plane of the 




OBLIQUITY OF THE ECLIPTIC. 399 

examined by Mr. Stockwell, and the results at which he has 
arrived are almost identical with those of Laplace. "The 
mean value of the obliquity," he says, ** of both the apparent 
and fixed ecliptics to the equator is 23° 17' 17". The limits 
of the obliquity of the apparent ecliptic to the equator are 
24° 35' 58" and 21° 58' 36" ; whence it follows that the greatest 
and least declinations of the sun at the solstices can never differ 
from each other to any greater extent than 2° 37' 22"." * 

This change will but slightly affect the climate of the tempo- 
rate regions, but it will exercise a very considerable influence on 
the climate of the polar regions. According to Mr. Meech,t if 
365-24 thermal days represent the present total annual quantity 
of heat received at the equator from the sun, 151-69 thermal days 
will represent the quantity received at the poles. Adopting his 
method of calculation, it turns out that when the obliquity of 
the ecliptic is at the maximum assigned by Laplace the quantity 
received at the equator would be 363*51 thermal days, and at 
the poles 160*04 thermal days. The equator would therefore 
receive 1*73 thermal days less heat, and the poles 8*45 thermal 
days more heat than at present. 

ecliptic, and has arrived at resnlts differing considerably from those of Laplace ; 
viz., t>iat the variAtion may amount to 4^ 52', whereas, occording to Laplace, it 
amounts to onl^ 1^ 21'. I fear they are comparing things that are totally 
different ; viz., the variation of the plane of the ecliptic in relation to its mean 
position with its variation in relation to the equator. Laplace estimated that 
the plane of the ecliptic would oscillate to the extent of 4* 53' 33* on each side of 
its mean position, a result almost identical with that of Leverrier, who makes it 
4"* 51' 42". But neither of these geometricians ever imagined that the ecliptic 
could change in relation to the equator to even one-third of that amount. 

Luplace demon.sirattid that the change in the plane of the ecliptic affected the 
position of the equator, causing it to vary along with it, so that the equator 
could never possibly recede further thHn 1° 22' 34* from its mean position in 
relation to the ecliptic {** Mteanique Ctleste,*' vol. ii.,p. 85C, Bowditch's Trans 
lution ; see also Laplace's memoir, **8ur les Variations de I'Obliquile de 
r£cliptique," Connais^ance des Ttnipa for 1827« p. 234), and I am not aware that 
Leverrier has arrived at a different conclusion. 

• Memoir on the Secular Variations of the Elements of the Orbits of tbs 
PlanetH, ''Smithsonian Contributions to Knowledge,'* vol. xvii. 

t ** SSmilhsouian Contributions to Knowledge," vol. ix. 



CLIMATE AND TIME. 



avau, UKovn or mm » rut. 



Amomt in 18D1. 
OI»liq[Bit]r»*>18'. 


AjBouut rt 
M"60rM*. 




Ijttitodo. 

40 
70 
80 
90 1 


Thenniil dayi. 
866 24 
2h8-66 
173-04 
166*63 
16169 


Thermal dayt. 
363-61 
288-32 
179-14 
164-63 
160-04 


Thennal dMi. 
-l-7> 
-0-2S 
-f 6-10 
4-8-00 
+ 8-46 



When the obliquity was at a maximum, the poIeB woald 
therefore be receiving 19 rays for every 18 they are leoeiTing 
at present. The poles would then be receiving nearly as much 
heat as latitude 76^ is receiving at present. 

The increase of obliquity would not sensibly affect the polar 
winter. It is true that it would slightly increase the breadth 
of the frigid zone, but the leugth of the winter at the poles 
would remain unaffected. After the sun disappears below the 
horizon his rays are completely cut off, so that a Airther descent 
of 1^ 22' 34'' would make no material difference in the climate. 
In the temperate regions the sim's altitude at the winter solstice 
would be 1" 22' 34" less than at present. This would slightly 
increase the cold of winter in those regions. But the increase 
in the amount of heat received by the polar regions would 
materially affect the condition of the polar summer. What, 
then, is the rise of temperature at the poles which would result 
from the increase of 8*45 thermal days in the total amount 
received from the sun ? 

An increase of 8*45 thermal days, or 1-lSth of the total 
quantity received from the sun, according to the mode of cal- 
culation adopted in Chap. II. would produce, all other things 
being equal, a rise in the mean annual temperature equal 
to 14^ or 15^. 

According to Professor Dove* there is a difference of 7^*6 
between the mean annual temperature of latitude 76^ and the 

• **Di8lributi«'n of ITcut on the Surfuce of tbe Globe/' p. 14. 



OBUQUITY OF THE ECLIPTIC. 401 

pole ; the temperature of the former being 9^-8, and that of tiie 
latter 2^*2. Since it follows that when the obliquity of the 
ecliptic is at a maximum the poles would receive about as much 
heat per annum as latitude 76° receiyes at present, it may be 
supposed that the temperature of the poles at that period ought 
to be no higher than that of latitude 76° at the present time. 
A little consideration will, however, show that this by no means 
follows. Professor Dove's Tables represent correctly the mean 
annual temperature corresponding to every tenth degree of 
latitude from the equator to the pole. But it must be observed 
that the rate at which the temperature diminishes from the 
equator io the pole is not proportionate to the decrease in the 
total quantity of heat received from the sun as we pass firom 
the equator to the pole. Were the mean annual temperature 
of the various latitudes proportionate to the amount of direct 
heat received, the equator would be much warmer than it 
actually is at present, and the poles much colder. The reason 
of this, as has been shown in Chapter II., is perfectly obvious. 
There is a constant transferrence of Aen^ firom the equator to the 
poles, and of cold from the poles to the equator. The warm 
water of the equator is constantly flowing towards the poles, 
and the cold water at the poles is constantly flowing to the 
equator. The same is the case in regazd to the aerial 
currents. Consequently a great portion of the direct heat of 
the sun goes, not to raise the temperature of the equator, but to 
heat the poles. And, on the other hand, the cold materials at 
the poles are transferred to the equator, and thus lower the 
temperature of that part of the globe to a great extent. The 
present difference of temperature between lat. 76° and the 
pole, determined according to the rate at which the temperature 
is found to diminish between the equator and the pole, amounts 
to only about 7° or 8°. But were there no mutual transferrence 
of warm and cold materials between the equatorial and polar 
regions, and were the temperature of each latitude to depend 
solely upon the direct rays of the sun, the difference would hx 
exceed that amount. 



4M 



CLIMATE AND TIME. 



Kow, when the obliquity of the ecliptic Iras at its 
limit, and the poles receiving about l-18th more direct best 
from the Bun than at present, the increase of temperatue dus 
to this increase of heat would be far more than 7^ or 8^. It 
would probably be nearly double that amount. 

We may, therefore, conclude that when the obliquity of flw 
ecliptic was at a maximum, and the poles were reoeiYing l-^lStL 
more heat than at present, the temperature of the polos ooght 
to have been about 14^ or 15^ warmer than at the present day, 
provided^ of eaurse, that this extra hea teas emphyed whaOg m 
raking the temperature. Were the polar regions free from snow 
and ice, the greater portion of the extra heat wonld go to raise 
the temperature. But as those regions are covered with snow 
and ice, the extra heat would have no effect in raising the tem- 
perature, but would simply melt the snow and ice. The ice- 
covered surface upon which the rays fell could never rise above 
32^. At the period under consideration, the total annual 
quantity of ice melted at the poles would be 1-1 8th more than 
at present. 

The general effect which the change in the obliquity of the 
ecliptic would have upon the climato of the polar regions when 
combined with the effects resulting from the eccentricity of the 
earth's orbit would be this : — When the eccentricity was at a 
very high value, the hemisphere whose winter occurred in the 
aphelion (for physical reasons, which have already been dis- 
cussed) * would be under a condition of glaciation, while the 
other hemisphere, having its winter in perihelion, would be 
enjoying a warm and equable climate. When the obliquity of 
the ecliptic was at a maximum, and l-18th more heat falling at 
the poles than at present, the effect would be to modify to a 
great extent the rigour of the glaciation in the polar zone of 
the hemisphere under a glacial condition, and, on the othet 
hand, to produce a more rapid melting of the ice on the oiH^i 
hemisphere enjoying the equable climate. The effects of ec-> 
oentricity and obliquity thus combined would probably com- 

• Chapter IV. 




OBLIQUITY OF THE ECLIPTIC. 403 

pletely remove the polar ice-cap from off the latter hemisphere^ 
and forest-trees might then grow *at the pole. Again, when 
the obliquity was at its minimum condition and less heat reach- 
ing the poles than at present, the glaciation of the former 
hemisphere would be increased and the warmth of the latter 
diminished. 

The Influetwe of Change in t/te Obliquity of the Ecliptic on the 
Level of the Sea. — One very remarkable effect which seems to 
result indirectly from a variation of the obliquity under certain 
conditions, is an influence on the level of the sea. As this pro- 
bably may have had something to do with those recent changes 
of sea-level ^4th which the history of the submarine forests and 
raised beaches have made us all so familiar, it may be of interest 
to enter at some length into this part of this subject. 

It appears almost certain that at the time when the northern 
winter solstice was in the aphelion last, a rise of the sea on the 
northern hemisphere to a considerable nimiber of feet must 
have taken place from the combined effect of eccentricity and 
obliquity. About 11,700 years ago, the northern winter sol- 
stice was in the aphelion. The eccentricity at that time was 
'0187, being somewhat greater than it is now ; but the winters 
occurring in aphelion instead of, as now, in perihelion, they 
would on that accoimt be probably 10° or 15° colder than they 
are at the present day. It is probable, also, for reasons stated 
in a previous chapter, that the Ghilf-stream at that time would 
be considerably less than now. This would tend to lower the 
temperature to a still greater extent. As snow instead of rain 
must have fallen during winter to a greater extent than at pre- 
sent, this no doubt must have produced a slight increase in the 
quantity of ice on the northern hemisphere had no other cause 
come into operation. But the condition of things, wo have 
every reason to believe, must have been aflectcd by the greater 
obliquity of the ecliptic at that period. We have no formula, 
except, perhaps, that given by Mr. Stockwell, from which to 
determine with perfect accuracy the extent of the obliquity at 
a period so remote as the one under consideration. If we adopt 



f04 CLIMATE AND TIME. 

fclie formula giTen by Struve and Peten, which agiees pxotty 
nearly with that obtained from Mr. Stookwell's fbrmida» we 
have the obliquity at a maximum about the time that the eol* 
stioe-point was in the aphelion. The formula given by Lever- 
lier places the maximum somewhat later. At all events, we 
cannot be far from the truth in assuming that at the time the 
northern winter solstice was in the aphelion, the obliquity of 
the ecliptic would be about a maximum, and that since then it 
has been gradually diminishing. It is evident, then, that the 
anuual amount of heat received by the arctic regions, and espe- 
cially about the polo, would be considerably greater than at 
present. And as the heat received on those regions is chiefly 
employed in melting the ice, it is probable that the eztn 
amount of ice which would then be melted in the arctic regions 
would prevent that sliglit increase of ice which would otherw^'se 
have resulted in consequence of the winter occurring in the 
aphelion. The winters at that period would be colder than 
they are nt present, but the total quantity of ice on the northern 
hemisphere would not probably be greater. 

Let us now turn to the southern hemisphere. As the 
southern winter would then occur in the perihelion, this would 
tend to produce a slight decrease in the quantity of ice on the 
southern hemisphere. But on this hemisphere the effects of 
eccentricity would not, as on the northern hemisphere, be com- 
pensated by those of obliquity ; for both causes would here 
tend to produce the same eflect ; namely, a melting of the ice 
in the antarctic regions. 

It is probiible that at this time the quantity of warm water 
flowing from the equatorial regions into the Southern Ocean 
would be much greater than at present. This would tend to 
raise the temperature of the air of the antarctic regions, and 
thus assist in melting the ice. These causes, combined with 
the great increase of heat resulting from the change of obli- 
quity, would tend to diminish to a considerable extent the 
quantity of ice on the southern hemisphere. I think we may 
assume that the slight increase of eccentricity at that period. 




OBLIQUITY OF THE ECLIPTIC. ^s 

the occurrenoe of the southern winter in perihelion, and the 
extra quantity of warm water flowing from the equatorial to 
the antarotio regions, would produce an effect on the south 
polar ice-cap eqiial to that produced by the increase in the 
obliquity of the ecliptic. It would, therefore, follow that for 
every eighteen pounds of ice melted annually at present at the 
south pole twenty pounds would then be melted. 

Let us now consider the effect that this condition of things 
would have upon the level of the sea. It would evidently tend 
to produce an elevation of the sea-level on the northern hemi- 
sphere in two ways. Ist. The addition to the sea occasioned 
by the melting of the ice from off the antarctic land would 
tend to raise the general level of the sea. 2Qdly. The removal 
of the ice would also tend to shift the earth's centre of gravity 
to the north of its present position — and as the sea must shift 
along with the centre, a rise of the sea on the northern hemi- 
sphere would necessarily take place. 

The question naturally suggests itself, might not the last rise 
of the sea, relative to the land, have resulted from this cause P 
We know that during the period of the 25-foot beach, the time 
when the estuarine mud, which now forms the rich soil of the 
Carses of the Forth and Tay, was deposited, the sea, in rela- 
tion to the land, stood at least 20 or 30 feet higher than at 
present. But immediately prior to this period we have the age 
of the submarine forests and peat-beds, when the sea relative 
to the land stood lower than it does now. We know also that 
these changes of level were not mere local aSiurs. There 
seems every reason to believe that our Oarse clay, as Mr. 
Fisher states, is the equivalent of the marine mud, with Scro* 
bicuhria, which covers the submarine forests of England.* And 
on the other hand, those submarine forests are not confined to 
one locality. "They may be traced,'' says Mr. Jamieson, 
'^ round the whole of Britain and Ireland, from Orkney to 
Cornwall, from Mayo to the shores of Fife, and even, it would 
seem, along a great part of the western sea-board of Europe^ 

* Quart. Joam. Geol. Soc., Jane, 1866, p. 664. 



fo6 



CLIMATE AND TIME. 






■ 
I 
1 

:? 



i 



M if they bore witness to a period of wide-spraad deraiiaB 
when Ireland and Britain, with all its nmnerons islanclB^ Ibnnd 
one mass of dry land, united to the continent, and stretbhini 
oat into the Atlantic."* '^ These submarine forests," Tenuoki 
De la Beche, also, "are to be found under the same genen] 
condition from the shores of ScandinaTia to those of E^mui 
and Portugal, and around the British islands."t Those buried 
forests are not confined to Europe, but are found in the Tallej 
of the Mississippi and in Nova Scotia, and other parts of Nortli 
America. And again, the strata which underiie those foresti 
and peat-beds bear witness to the fact of a prerious elevation d 
the sea-level. In short, we have evidence of a number of oscil- 
lations of sea-level during post-tertiary times. % 

Had there been only one rise of the land relative to tiie sea- 
lovel, or one depression, it might quite reasonably, as alreadj 
remarked, have been attributed to an upheaval or a sinking oi 
the ground, occasioned by some volcanic, chemical, or othei 
agency. But certainly those repeated oscillations of sea-level 
extending as they do over so 'v^'ide an area, look more like i 
rising and sinking of the sea than of the land. But, be this ai 
it may, since it is now established, I presume, beyond contro- 
versy, that the old notion that the general level of the set 
remains permanent, and that the changes must be all attri< 
butcd to the land is wholly incorrect, and that the sea, as wel 
as the land, is subject to changes of level, it is certainly quiU 
legitimate to consider whether the last elevation of the sea 
level relatively to the land may not have resulted from thi 
rising of the sea rather than from the sinking of the land, ii 
short, whether it may not be attributed to the cause we are nov 
considering. The fact that those raised beaches and terrace 
are found at so many different heights, and also so discon 

* Quart. Joum. Oeol. Soc., vol. xxi., p. 186. 

t «* Geological Observer/* p. 446. See also Mr. James Geikie's valaalil 
Bf emoir, ** On the Buried Forests and Peat Mosses of Scotland." Tram, of th 
Royal Society of Edinburgh, vol. xziv., and Chambers* " .Ancient Sea-Margins.' 

X See Lyrirs «* Antiquity of Man," Second Edition, p. 282 ; " Elementi," 8ixt] 
Edition, p. 162. 



OBLIQUITY OF THE ECLIPTIC. 407 

tinuously along our coasts, miglit be urged as an objection to 
the opinion that they were due to changes in the level of the 
sea itself. Space will not permit me to enter upon the discus- 
sion of this point at present; but it may be stated that this 
objection is more apparent than real. It by no means follows 
that beaches of the same age must be at the Bame level. This 
has been shown very clearly by Mr. W. Pengelly in a paper 
on '^ Raised Beaches/' read before the British Association at 
Nottingham, 1866. 

We have, as I think, evidence amountiug to almost absolute 
certainty that 11,700 yeais ago the general sea-level on the 
northern hemisphere must have been higher than at present. 
And in order to determine the question of the 25-foot beach, we 
have merely to consider whether a rise to something like this 
extent probably took place at the period in question. We have 
at present no means of determining the exact extent of the rise 
which must have taken place at that period, for we cannot tell 
what quantity of ice was then melted off the antarctic regions. 
But we have the means of making a very rough estimate, which, 
at least, may enable us to determine whether a rise of some 20 
or 30 feet may not possibly have taken place. 

If we assume that the southern ice-cap extends on an average 
down to lat. 70^, we shall have an area equal to it\tt of the 
entire surface of the globe. The proportion of land to that of 
water, taking into account the antarctic continent, is as 526 to 
1272. The southern ice-cap will therefore be equal to W-^r of 
the area covered by water. The density of ice to that of water 
being taken at '92 to 1, it follows that 25 feet 6 inches of ice 
melted from off the face of the antarctic continent would raise 
the level of the ocean one foot. If 470 feet were melted off— 
and this is by no means an extravagant supposition, when we 
reflect that for every 18 pounds of ice presently melted an addi- 
tional pound or two pounds, or perhaps more, would then be 
melted, and that for many ages in succession — the water thus 
produced from the melted ice would raise the level of the sea 
18 feet 5 inches. The removal of the 470 feet of solid ice — ' 



4o8 CLIMATE AND TIME. 

which must be but a yery small fraction of the total quantitj of 
ice lying npon the antarctic continent — ^woold shift the eardi's 
centre of gravity about 7 feet to the north of its present posi« 
tion. The shifting of the centre of gravity would cause ihe sea 
to sink on the southern hemisphere and rise on the northenb 
And the quantity of water thus transferred firom the southern 
hemisphere to the northern would carry the centre of gravity 
about one foot further, and thus give a total displacement of 
the centre to the extent of about 8 feet. The sea would there- 
fore rise about 8 feet at the North Pole, and in the latitude of Edin- 
burgh about 6 feet 7 inches. This, added to the rise of 18 feet 
5 inches, occasionedby the melting of the ice, would give 25 feet 
as the total rise in the latitude of Scotland 11,700 years ago. 

Each square foot of surface at the poles 11,700 years ago 
would be receiving 18,223,100 foot-pounds more of heat 
annually than at present. If we deduct 22 per cent, as the 
amount absorbed in passing through the atmosphere, we have 
14,214,000 foot-pounds. This would be sufficient to melt 2*26 
feet of ice. But if 50, instead of 22, per cent, were cut off, 
1*45 cubic feet would be melted. In this case the 470 feet of 
ice would be melted, independently of the effects of eccentricity, 
in about 320 years. And supposing that only one-fourth part 
of the extra heat reached the ground, 470 feet of ice would be 
removed in about 640 years. 

As to the exact time that the obliquity was at a maximum, 
previous to that of 11,700 years ago, our uncertainty is still 
greater. If we are permitted to assume that the ecliptic passes 
from its maximum to its minimum state and back to its maxi- 
mum again with anything like uniformity, at the rate assigned 
by Leverrier and others, the obliquity would not be far from a 
maximum about 60,000 years ago. Taking the rate of precession 
at 60"*21129, and assuming it to be uniform — which it probably 
is not — the winter solstice would be in the aphelion about 
61,300 years ago.* In short, it seems not at all improbable that 

* In order to determine the position of the BoUtice-point in relation to the 
tphelioD) it will not do to assume, as is commonly doue, that the point makes e 



OBLIQUITY OF THE ECLIPTIC. 409 

at the time the solstice-point was in the aphelion, the oUiqnitjr 
of the ecliptic would not be £ir from its maximum state. But at 
that time the value of the eccentricity was 0*023, instead of 
0*0187, its value at the last period. Consequently the rise of 
the sea would probably be somewhat greater than it was 11,700 
years ago. Might not this be the period of the 40-foot 
beach P In this case 11,000 or 12,000 years would be the age 
of the 25-foot beach, and 60,000 years the age of the 40-feet 
beach. 

About 22,000 years ago the winter solstice was in the peri- 
helion, and as the eccentricity was then somewhat greater than 
it is at present, the winters would be a little warmer and the 
climate more equable than it is at the present day. This 
perhaps might be the period of the submerged forests and lower 
peut-beds which underlie the Carse days, Scrobwularia mud, 
and other deposits belonging to the age of the 26-feet beach. 
At any rate it is perfectly certain that a condition of climate 
at this period prevailed exceedingly favourable to the growth 
of peat. It follows also that at this time, owing to a greater 
accumulation of ice on the southern hemisphere, the sea-level 
would be a few feet lower than at present, and that forests and 
peat may have then grown on places which are now under the 

sea-level. 

For a few thousand years before and after 11,700 years ago, 
when the winter solstice was evidently not far from the 
aphelion, and the sea standing considerably above its present 
level, would probably, as we have already stated, be the time 
when the Carse clays and other recent deposits lying above 
tbo present level of the river were formed. And it is also a 
singular fact that the condition of things at that period must 

revolution from aphelion to aphelion in any regular given period, inch aa 21,000 
yeara ; for it ia perfectly evident that owing to the great irregularis in the 
motion of the aphelion, no two revointiont wiU prohahly he perfbrmed in the 
ifime lAni;th of period. For example^ the winter solstice was in the aphelion 
ahout the following dates : 11»700, 83,800, and 61,800 yean ago. Here are two 
consecutive revolutions* the one performed in 21,600 years and the other in 
28,000 years ; the difference in the length of the two periods amowntiiig te at 
fewer thun 6,400 years. 



4IO CLIMATE AND TIME. 

hare been exceedingly favourable to the fomuttiDii of sogIl 
estoarine deposits ; for at that time the winter tempermture of 
oar island^ as has been already shown, would be €ton8idera.Uy 
lower than at present, and, consequently, during that season, 
snow, to a much larger extent than nov", would fall instead of , 
rain. The melting of the winter's accumulation of snow on 
the approach of summer would necessarily produce great floods^ 
similar to what occur in the northern parts of Asia and 
America at the present day from this very same cause. The 
loose upper soil would bo carried down by those floods and 
deposited in the estuaries of our rivers. 

The foregoing is a rough and imperfect sketch of the history 
of the climate and the physical conditions of our globe for the 
past 60,000 years, in so far as physical and cosmical considera^ 
tions seem to afibrd us information on the subject, and its 
striking agreement with that derived from geological sources 
is an additional evidence in favour of the opinion that geological 
and cosmical phenomena are physically related by a bond of 
causation. 

Lieutenant' Colon4^l Dray 8on^ 9 Theory of the CatiseoftJie Glacial 
Epoch. — In a paper read before the Geological Society by Lieu- 
tenant-Colonel Drayson, B.. A., on the 22nd February, 1871,* that 
author states, that after calculating from the recorded positions 
of the pole of the heavens during the last 2,000 years, he finds 
the pole of the ecliptic is not the centre of the circle traced by 
the pole of the heavens. The pole of the heavens, he considers, 
describes a circle round a point 6^ distant from the pole of the 
ecliptic and 29^ 25' 47'' from the pole of the heavens, and that 
about 13,700 years b.c. the angular distance of the two poles 
was 36° 25' 47". This would bring the Arctic Circle down to 
latitude 54° 34' 13" N. I fear that this is a conclusion that will 
not be generally accepted by those familiar with celestial 
mechanics. But, be this as it may, my present object is not to 
discuss the astronomical part of Colonel Drayson's theory, but 

• Quart. Joum. Geol. Soc, toI. zxvit., p. 232. See alio *' The Lati GImmI 
of Geology/* hy the aaice author. 




OBLIQUITY OF THE ECLIPTIC. 41 1 

to consider whetker the oonclusions which he deduces from his 
theory in regard to the cause of the glacial epoch be legiti- 
mate or not. Assuming for argument's sake that the obliquity 
of the ecliptic can possibly reach to 35° or 36°, so as to bring 
the Arctic Circle down to the centre of England, would this 
account for the glacial epoch P Colonel Drayson concludes 
that the shifting of the Arctic Circle down to the latitude of 
England would induce here a condition of climate similar to 
that which obtains in arctic regions. This seems to be the 
radical error of the theory. It is perfectly true that were 
the Arctic Circle brought down to latitude 64° 36' part of our 
island would be in the arctic regions, but it does not on that 
account follow that our island would be subjected to an arctio 
climate. 

The polar regions owe their cold not to the obliquity of the 
ecliptic, but to their distance from the equator. Indeed were 
it not for obliquity those regions would be much colder than 
they really are, and an increase of obliquity, instead of 
increasing their cold, would really make them warmer. The 
general effect of obliquity, as we have seen, is to diminish the 
amount of heat received in equatorial and tropical regions, and 
to increase it in the polar and temperate regions. The greater 
the obliquity, and, consequently, the farther the sun recedes 
from the equator, the smaller is the quantity of heat received 
by equatorial regions, and the greater the amount bestowed 
on polar and temperate regions. If, for example, we represent 
the present amount of heat received from the sxm at the equator 
on a given surface at 100 parts, 42*47 parts will then represent 
the amount received at the poles on the same given surface. 
But were the obliquity increased to 35° the amount received 
at the equator would bo reduced to 94'93 parts, and that at the 
polos increased to 59'81 ; being an increase at the poles of 
nearly one half. At latitude 60° the present quantity is equal 
to 57 parts; but about 63 parts would be received were the 
obliquity increased to 35°, It therefore follows that although 
the Arctic Circle were brought down to the latitude of London so 



411 CLIMATE AND TIME. 

ihat the British islandB would becomeapart of ihearctiongiau^ 
the mean temperature of these islands would not be lowered^ 
but the reverse. The winters would no doubt be colder than 
they are at present, but the cold of winter would be fiir more 
than compensated for by the heat of summer. It is not a fiur 
representation of the state of things, merely to say that an 
increase of obliquity tends to make the winters colder and the 
summers hotter, for it affects the simmier heat £eu* more than 
it does the winter cold. And the greater the obliquity the 
more does the increase of heat during sunmier exceed the 
decrease during winter. This is obvious because the greater 
the obliquity the greater the total annual amount of heat 
received. 

If an increase of obliquity tended to produce an increase of 
ice in temperate and polar regions, and thus to lead to a glacial 
epoch, then the greater the obliquity the greater would be the 
tendency to produce such an effect. Conceive, then, the obli- 
quity to go on increasing until it ultimately reached its absolute 
limit, 90°, and the earth's axis to coincide with the plane of 
the ecliptic. The Arctic Circle would then extend to the 
equator. Would this produce a glacial epoch ? Certainly 
not. A square foot of surface at the poles would then be 
receiving as much heat per annum as a square foot at ^<fi 
equator at present, supposing the sun remained on the equator 
during the entire year. Less heat, however, would be reaching 
the equatorial regions than now. At present, as wo have just 
seen, the annual quantity of heat received at either pole is to 
that received at the equator as 42*47 to 100 ; but at the period 
under consideration the poles would he actually obtaining one- 
half more heat than the equator. The amount received per 
square foot at the poles, to that received per square foot at the 
equator, would be in the ratio of half the circumference of a 
circle to its diameter, or as 1*5708 to 1. But merely to say 
that the poles would be receiving more heat per annum than 
the equator is at present, does not convey a correct idea of the 
excessive heat which the poles would then have to endure ; f(U 



OBLIQUITY OF THE ECLIPTIC. 413 

it must be borne in mind that the heat reaching the equator 
is spread over the whole year, whereas the poles would get 
their total amount during the six mouths of their summer. 
Consequently, for six months in the year the poles would be 
obtaining far more than double the quantity of heat received at 
present by the equator during the same length of time, and 
more than three times the quantity then received by the 
equator. The amount reaching the pole during the six months 
to that reaching the equator would be as 3'1416 to 1. 

At the equator twelve hours' darkness alternates with twdVe 
hours' sunshine, and this prevents the temperature from rising 
excessively high ; but at the poles it would be continuous sun- 
shine for six months without the ground having an opportunity 
of cooling for a single hour. At the summer solstice, when 
the sun would be in the zenith of the pole, the amount of heat 
received there every twenty-four hours would actually be 
nearly three-and-a-quarter times greater than that presently 
received at the equator. Now what holds true with r^;ard to 
the poles would hold equally true, though to a lesser extent, 
of polar and temperate regions. We can form but a very in- 
adequate idea of the condition of things which would result 
from such an enormous increase of heat. Nothing living on 
the face of the globe could exist in polar regions under so 
fearful a temperature as would then prevail during summer 
months. How absurd would it be to suppose that this con- 
dition of things would tend to produce a glacial epooh I Not 
only would every particle of ice in polar regions be dissipated, 
but the very seas around the pole would be, for several months 
in the year, at the boiling point. 

If it could be shown from physical principles — ^which, to say 
the least, is highly improbable-— that the obliquity of the 
ecliptic could ever have been as great as 35^, it would to a 
very considerable extent account for the comparative absence 
of ice in Greenland and other regions in high latitudes, such 
as we know was the case during the Carboniferous, Miocene, 
and other periods. But although a great increase of obliquity 



4t4 CLIMATE AND TIME. 

migbt cause a melting of the ice^ yet it oould not produoe tiuft 
mild condition of climate which we know prevailed in Iii^ 
latitudes during those periods ; while no increase of obliqiiitj, 
however great, could in any way tend to produce a glaoU 
epoch. 

Colonel Drayson, however, seema to admit that thia great 
increase of obliquity would make our summers much wanmer 
than they are at present. How, then, according to his iheoiji 
is the glacial epoch accounted forP The following is the 
author's explanation as stated in his own words : — 

*' At the date 13,700 b.c. the some conditions appear to have 
prevailed down to about 54^ of latitude during winter as regards 
the sun being only a few degrees above the horizon. We are, 
then, warranted in concluding that the same climate prevailed 
down to 54° of latitude as now exists in winter down to 67° of 
latitude. 

" Thus in the greater part of England and Wales, and in the 
whole of Soctland, icebergs of large size would be formed each 
winter; every river and stream would be frozen and blocked 
with ice, the whole country would be covered with a mantle of 
snow and ice, and those creatures which could neither migrate 
nor endure the cold of an arctic climate would be exterminated." 
— " The Last Glacial Epoch," p. 146. 

'' At the summer solstice the midday altitude of the sun for 
the latitude 54° would be about 71^°, an altitude equal to that 
which the sun now attains in the south of Italy, the south of 
Spain, and in all localities having a latitude of about 40°." 

" There would, however, be this singular difference from 
present conditions, that in latitude 54° the sun at the period of 
the summer solstice would remain the whole twenty-four hours 
above the horizon; a fact which would give extreme heat to 
those very regions which, six months previously, had been 
subjected to an arctic cold. Not only would this greatly 
increased heat prevail in the latitude of 54°, but the aun'a 
altitude would be 12° greater at midday in midsummer, and 
also 12° greater at midnight in high northern latitudes, than 



OBLIQUITY OF THE ECLIPTIC. 415 

it ever attains now ; consequently the heat would be far greater 
than at present, and high northern regions, even around tho 
pole itself, would be subjected to a heat during summer far 
greater than any which now ever exists in those localities. T,h© _ 
natural consequence would be, that the icebergs and ice which 
had during the severe winter accumulated in high latitudes 
would be rapidly thawed by this heat" (p. 148). 

" Each winter the whole northern and southern hemispheres 
would be one mass of ice ; each summer nearly the whole of 
the ice of each hemisphere would be melted and dispersed " 
(p. 150). 

• According to this theory, not only is the whole country 
covered each winter with a continuous mass of ice, but large 
icebergs are formed during that short season, and when the 
summer heat sets in all is melted away. Here we have a mis- 
apprehension not only as to the actual condition of things 
during the glacial epoch, but even as to the way in which ice- 
bergs and land-ice are formed. Icebergs are formed from 
land- ice, but land-ice is not formed during a single winter, much 
less a mass of sufficient thickness to produce icebergs. Land- 
ice of this thickness requires the accumulated snows of centuries 
for its production. All that we could really have, according to 
this theory, would be a thick covering of snow during winter, 
which would entirely disappear during summer, so that there 
could be no land-ice. 

J/r. Thomas Belt's Theory. — The theory that the glacial 
epoch rcsidted from a great increase in the obliquity of the 
ecliptic has recently been advocated by Mr. Thomas Belt.* 
His conceptions on the subject, however, appear to me to be 
even more iiTeconcilable with physics than those we have been 
considering. Lieutenant-Colonel Drayson admits that the in- 
crease of heat to polar regions resulting from the great increase 
of obliquity would dissipate the ice there, but Mr. Belt does not 
even admit that an increase of obliquity would bring with it 
an increase of heat, far less that it would melt the polar ice. 

* Quart. Journ. of Science, October, 1874< 
19 



4i6 CLIMATE AND TIME. 

On the contrary^ he maintains that the tendency of oUiquily it 
to increase the rigour of polar dimate, and that this is the 
reason ''that now around the poles some lands are hemg 
gkJiatedy for excepting for that obliquity snow and ice would 
not accumulate, excepting on mountain chains." " Thus^^ he 
saysy ''there exist glacial conditions at present around the 
polesy due primarily to the obliquity of the ediptic" And he 
also maintains that if there were no obliquity and the earth's 
axis were perpendicular to the plane of its orbit, an eternal 
"spring would reign around the arctic circle,'' and that 
" under such circumstances the piling up of snow, or even its 
production at the sea-level, would be impossible, excepting per- 
haps in the immediate neighbourhood of the poles, where the 
rays of the sun would have but little heating power from its 
small altitude/' 

Mr. Belt has apparently been led to these strange conclu- 
sions by the following singular misapprehension of the effect, 
of obliquity on the distribution of the sun's heat over the globes 
'* The obliquity of the ecliptic," he remarks, " doe% not affect the 
mean amount of heat received at any one point from the sun, but it 
causes the Le.it and the cold to predominate at different seasons 
of the year." 

It is not necessary to dwell further on the absurdity of the 
supposition that an increase of obliquity can possibly account 
for the glacial epoch, but we may in a few words consider 
whether a decrease of obliquity would mitigate the climate and 
remove the snow from polar regions. Supposing obliquity to 
disappear and the earth's axis to become perpendicular to the 
plane of its orbit, it is perfectly true that day and night woidd 
be equal all over the globe, but then the quantity of heat 
received by the polar regions would be far less than at present. 
It is well known that at present at the equinoxes, when day 
and night are equal, snow and not rain prevails in the arctic 
regions, and can we suppose it could be otherwise in the cate 
under consideration ? How, we may well ask, could these regions^ 
ived of their summer, get rid of their snow and ice P 




OBLIQUITY OF THE ECLIPTIC. 417 

But even suppoaiiig it could be shown that a change in the 
obliquity of the ecliptic to the extent assumed by Mr. Belt and 
Lieutenant-Colonel Drayson would produce a glacial epoch, still 
the assumption of such a change is one which physical astronomy 
will not permit. Mr. Belt does not appear to dispute the 
accuracy of the methods by which it is proved that the varia- 
tions of obliquity are confined within narrow limits ; but he 
maintains that physical astronomers in making their calcula- 
tions have left out of account some circumstances which materi- 
ally affect the problem. These, according to Mr. Belt, are the 
following : — (1) Upheavals and subsidences of the land which 
may have taken place in past ages. (2) The unequal distribu- 
tion of sea and land on the globe. (3) The fieu^t that the equa- 
torial protuberance is not a regular one, ** but approaches in a 
general outline to an ellipse, of which the greater diameter is 
two miles longer than the other.'' (4) The heaping up of ice 
around the poles during the glacial period. 

We may briefly consider whether any or all of these can 
sensibly affect the question at issue. In reference to the last- 
mentioned element, it is no doubt true that if an immense 
quantity of water were removed from the ocean and placed 
around the poles in the form of ice it would affect the obliquity 
of the ecliptic; but this is an element of change which is 
not available to Mr. Belt, because according to his theory the 
piling up of the ice is an effect which results from the change 
of obliquity. 

In reference to the difference of two miles in the equatorial 
diameters of the earth, the fact must be borne in mind that the 
longer diameter passes through nearly the centre of the great 
depression of the Pacific Ocean,* whereas the shorter diameter 
pusses through the opposite continents of Asia and America. 
JS'ow, when we take into consideration the fact that these con- 
tinents are not only two-and-a-half times denser than the ocean, 
but have a mean elevation of about 1,000 feet above the sea- 
level, it becomes perfectly obvious that the earth's mass must 

« The longer diameter pastes from long. 14" 23' E. to long. \W %T W. 




4i8 CLIMATE AND TIME. 

be pretty evenly distributed around its axis of rotatioiiy and 
that therefore the difference in the equatorial diameters can 
exercise no appreciable effect on the change of oUiquiiy. It 
follows also that the present arrangement of sea and land is the 
best that could be chosen to prevent disturbance of motion. 

That there ever were upheavals and depressions of the land 
of so enormous a magnitude as to lead to a change of obliquity to 
the extent assumed by Lieutenant-Colonel Drayson and Mr. Belt 
is what, I presume, few geologists would be willing to admit 
Suppose the great table-land of Thibet, with the Himalaya 
Moimtains, were to sink imder the sea, it would hardly produce 
any sensible effect on the obliquity of the ecliptio. Nay more ; 
supposing that all the land in the globe were sunk' under the 
sea-level, or the ocean beds converted into dry land, still this 
would not materially affect obliquity. The reason is very 
obvious. The equatorial bulge is so immense that those up- 
heavals and depressions would not to any great extent alter the 
oblate form of the earth. The only cause which could produce 
any sensible effect on obliquity, as has already been noticed, 
would be the removal of the water of the ocean and the piling 
of it up in the form of ice around the poles ; but this is a cause 
which is not available to Mr. Belt. 

Sir Charles LyelFs Theory, — I am also unable to agree with 
Sir Charles Lyell's conclusions in reference to the influence of 
the obliquity of the ecliptic on climate. Sir Charles says, " It 
may be remarked that if the obliquity of the ecliptic could ever 
be diminished to the extent of four degrees below its present 
inclination, such a deviation would bo of geological interest, in 
so far as it would cause the sun's light to be disseminated over 
a broader zone inside of the arctic and antarctic circles. Indeed, 
if the date of its occurrence in past time could be ascertained, 
this greater spread of the solar rays, implying a shortening of 
the polar night, might help in some slight degree to accoimt 
for a vegetation such as now characterizes lower latitudes, 
having had in the Miocene and Carboniferous periods a much 
wider rtinge towards the pole."* 

• *« Principleii/' vol. i., p. 294. Eleventh Edition. 



OBLIQUITY OF THE ECLIPTIC. 



419 



The effects, as we have seen, would be directly the reverse of 
what is here stated, yiz., the more the obliquity was diminished 
the lei% would the run's rays spread over the arctic and antarctic 
regions, and conversely the more the obliquity was increased 
the greater would be the amount of heat spread over polar 
latitudes. The farther the sun recedes from the equator, the 
greater becomes the ainount of heat diffused over the polar 
regions ; and if the obliquity could possibly attain its absolute 
limit (90^), it is obvious that the poles would then be receiving 
more heat than the equator is now. 



CHAPTEE XXVI. 



GOAL AX INTER-GLAaAL FORMATIOH. 

dinate of Coal Period Inter-i^lacul in Character. — Cool Plants indicate aa 
Equable, not a Tropic^ Climate. — Conditions necessair for Pnserratkm of 
Coal Plants. — Ofci^tations of S^a-lerel neceaearily implied. — "Why oar Goal- 
fields contain more than One Coal-seam. — Time required to form a Bed of 
Ci^. — W'hr Cv>al Strata contain so little e^-idenc-e of Ice-action. — Land 
H.it durir.*; C'.ul TciiM. — L- aiing Idea of tLe Theory. — Carboniferous 
Liincs:cno9>. 

An Liffr-^juicujl CV/;^»\V t/.e one It^f (fuiftd fur the Grotcth oj 
the Coal Plants, — Xo assertion, perhaps, could appear more im- 
probable, or is more opposed to all hitherto received theories, 
than the one that the plants which form our coal grew during a 
glaci:d epoch. But, nevertheless, if the theory of secular 
changes of oliTiiute, discussed in the foregoing chapters, be 
correct, wo have in warm inter-glacial periods \^as was pointed 
out SvVeral vears airo.* the verv condition of climate best 
suited f'»r the grt.»wth uf those kinds if trcts and vegetation 
of which our ct»td is C"Uijx>sod. It is the generally received 
opinion among b"t:i go-ilogists and b«>taiiists that the floral of 
the Cual period d-xs not indicate tlie existence of a tropical, 
but a moist, e<[u:il>lo, and temperate climate. ** It seems to 
have becume,'* savs Sir Charles Lvcll, *• a more and more 
received opinion that the coal plants do not on the whole 
indicate a climate resembling that now ei.j^'yt'd in the equa- 
torial zone. Tree-ferns range as far south as the southern 
parts of Xew Zealand, and Araucanian pines occur in Norfolk 
Island. A great preponderance of ferns and lycopodiuma 

♦ Phil. Mag. for Atigiut, 1854. 




COAL AN INTER-GLACIAL FORMATION. 411 

indicates moisture, equability of temperature, and freedom 
from frost, rather than intense heat."* 

Mr. Bobert Brown, the eminent botanist, considers that the 
rapid and great growth of many of the coal plants showed that 
they grew in swamps and shallow water of equable and genial 
temperature. 

" Generally speaking," says Professor Pago, " we find them 
resembling equisetums, marsh-grasses, reeds, club-mosses, tree- 
ferns, and coniferous trees ; and these in existing nature attain 
their maximum development in warm, temperate, and sub- 
tropical, rather than in equatorial regions. The Welling- 
tonias of California and the pines of Norfolk Island are 
more gigantic than the largest coniferous tree yet discovered in 

the coal-measures." t 

The Coal period was not only characterized by a great pre- 
ponderance over the present in the quantity of ferns growing, 
but also in tho number of diflFetont species. Our island pos- 
sesses only about 50 species, while no fewer than 140 species 
have been enumerated as having inhabited those few isolated 
places in England over which the coal has been worked. And 
Humboldt has shown that it is not in the hot, but in the moun- 
tainous, humid, and shady parts of the equatorial regions that 
the family of ferns produces the greatest number of species. 

'' Dr. Hooker thinks that a climate warmer than ours now 
is, would probably be indicated by the presence of an increased 
number of flowering plants, which would doubtless have been 
fossilized with the ferns ; whilst a lower temperature, equal to 
the mean cf tlie seasons note prevailingy would assimilate our 
climate to that of such cooler countries as are characterized by 
a disproportionate amount of ferns." + 

** The general opinion of the highest authorities," says 
Professor Hull, " appears to be that the climate did not 
resemble that of the equatorial regions, but was one in which 

• " Elementiry Geology," p. 399. 

t **The Past and TreHHTit Lif« of the Globe," p. 102. 

X ** Memoin of the Geological Suivey," voL ii., Part % p. 40i. 



fi2 CLIMATE AND TIME. 

the temperature was free from extremes ; the atmosphere beiiig 
warm and moist, somewhat resembling that of New Zealand 
and the surrounding islands, which we endeavour to imii^^ 
artificially in our hothouses. "• 

The enormous quantity of the carboniferous Tegetation shows 
also that the climate under which it grew could not have been 
of a tropical character, or it must have been decomposed by the 
heat. Peat, so abundant in temperate regions, is not to be 
found in the tropics. 

The condition most favourable to the presenration of vege- 
table remains, at least xmder the form of peat, is a cool, moist, 
and equable climate, such as prevails in tiie Falkland Islands 
at the present day. *<In these islands,'' says Mr. Darwin, 
** almost every kind of plant, even the coarse grass which 
covers the whole surface of the land, becomes converted into 
this substance." t 

From the evidence of geology we may reasonably infer that 
were the difference between our summer and winter tempera- 
ture nearly annihilated, and were we to enjoy an equable 
climate equal to, or perhaps a little above, the present mean 
annual temperature of our island, we should then have a 
climate similar to what prevailed during the Carboniferous 
epoch. 

But we have already seen that such must have been the 
character of our climate at the time that the eccentricity of 
the earth's orbit was at a maximum, and winter occurred when 
the earth was in the perihelion of its orbit. For, as we have 
already shown, the earth would in such a case be 14,212,700 
miles nearer to the sun in winter than in summer. This 
enormous difference, along with other causes which have been 
discussed, would almost extinguish the difference between 
summer and winter temperature. The alruost if not entire 
absence of ice and snow, resulting from this condition ol 
things, would, as has already been shown, tend to raise th# 

• " Coal FieldH of Great Britain/* p. 45. Third EdUiob. 

♦ *' Journal of lioseurc-lies," chap. xiii. 




COAL AN INTER-GLACIAL FORMATION. 413 

mean annual temperature of the climate higher than it is at 
present. 

Conditiofu necessary for the PreserwUion of the Coal Planis. — 
But in order to the formation of ooal^ it is not simply necessary 
to have a condition of climate suitable for the growth^ but also 
for the preservation, of a luxuriant yegetation. The yery 
existence of coal is as much due to the latter circumstance 
as to the former ; nay more, as we shall yet see, the &ct that 
a greater amount of coal belongs to the Carboniferous period 
than to any other, was evidently due not so much to a more 
extensive vegetable growth during that age, suited to form 
coal, as to the fact that that flora has been better preserved. 
Now, as will be presently shown, we have not merely in the 
warm periods of a glacial epoch a condition of climate best 
suited for the growth of coal plants, but we have also in the 
cold periods of such an epoch the condition most favourable for 
the preservation of those plants. 

One circumstance necessary for the preservation of plants is 
that they should have been covered over by a thick deposit of 
sand, mud, or day, and for this end it is necessary that the 
area upon which the plants grew should have become sub* 
merged. It is evident that unless the area had become 
submerged, the plants could not have been covered over with 
a thick deposit ; and, even supposing th^ had been covered 
over, they could not have escaped destruction from subaerial 
denudation unless the whole had been under water. Another 
condition favourable, if not essential, to the preservation of the 
plants, is that they should have been sulmierged in a cold and 
not in a warm sea. Assuming that the coal plants grew during 
a warm period of a glacial epoch, we have in the cold period 
which succeeded all the above conditions necessarily secured. 

It is now generally admitted that the coal trees grew near 
broad estuaries and on immense flat plains but little elevated 
above sea-level. But that the Lepidodendra, SigiUaruSf and 
other trees, of which our coal is almost wholly composed, grew 
on dry ground, elevated aboyo sea^level, and not in swamps and 



444 CLIMATE AND TIME. 

shallow water, as was at one time supposed, lias been coiidhi* 
sively established by the researches of Principal Dawscm and 
oQiers. After the growth of many generations of treeSt the 
jdain is eventually submerged xmder the sea, and the whole, 
through course of time, becomes covered over with thick 
deposits of sand, gravel, and other sediments carried down by 
■teeams firom the adjoining land. After this the submerged 
plain becomes again elevated above the sea-level, and forms 
the site of a second forest, which, after continuing to flourish 
for long centuries, is in turn destroyed by submergence, and, 
like the former, becomes covered over with deposits from the 
land. This alternate process of submergence and emergence 
goes on till we have a succession of buried forests one above 
another, with immense stratified deposits between. These 
buried forests ultimately become converted into beds of coaL 
This, I presume, is a fair representation of the generally 
admitted way in which our coal-beds had their origin. It is 
also worthy of notice that the stratified beds between the coal- 
seams are of marine and not of lacustrine origin. On this 
point I may quote the opinion of Professor Hull, a well-known 
authority on the subject : " Whilst admitting," he says, "the 
occasional presence of lacustrine strata associated with the 
coal-measures, I think we may conclude that the whole forma- 
tion has been essentially of marine and estuarine ^origin."* . 

Coal'beda nece89arily imply OaciUationa of Sea-level. — It may 
also be observed that each coal-seam indicates both an eleva- 
tion and a depression of the land. If, for example, there are 
six coal-seams, one above the other, this proves that the land 
must have been, at least, six times below and six times 
above sea-level. This repeated oscillation of the land has been 
regarded as a somewhat puzzling and singular circumstance. 
But if we assume coal to be an inter-glacial formation, this 
difficulty not only disappears, but all the various circumstances 
which we have been detailing are readily explained. We have 
to begin with a warm inter-glacial period, with a climate 

♦ " Coal Ficlda of Great Britain," p. 67. 



COAL AN INTER-GLACIAL FORMATION. 425 

specially suited for ihe growth of the coal trees. During thii 
period, as has been shown in the chapter on Submergence, the 
sea would be standing at a lower level than at present, laying 
bare large tracts of sea-bottom, on which would flourish the 
coal vegetation. This condition of things would continue for 
a period of 8,000 or 10,000 years, allowing the growth of many 
generations of trees. When the warm period came to a close, 
and the cold and glacial condition set in, the climate became 
unsuited for the growth of the coal plants. The sea would 
begin to rise, and the old sea-bottoms on which, during so long 
a period, the forests grew, would be submerged and become 
covered by sedimentary deposits brought down from the land. 
These forests becoming submerged in a cold sea, and buried 
under an immense mass of sediment, were then now protected 
from destruction, and in a position to become converted into 
coal. The cold continuing for a period of 10,000 years, or 
thereby, would be succeeded by another warm period, during 
which the submerged areas became again a land-surface, on 
which a second forest flourished for another 10,000 years, 
which in turn became submerged and buried under drift on 
the approach of the second cold period. This alternate pro- 
cess of submergence and emergence of the land, corresponding 
to the rise and fall of sea-level during the cold and warm 
periods, would continue so long as the eccentricity of the 
earth's orbit remained at a high value, till we might have, 
perhaps, five or six submerged forests, one above the other, 
and separated by great thicknesses of stratified deposits, these 
submerged forests being the coal-beds of the present day. 

It is probable that the forests of the Coal period would 
extend inland over the country, but only such portions as 
were slightly elevated above sea-level would be submerged 
and covered over by sediment and thus be preser\'ed, and 
ulti mutely become coal-seams. The process will be better 
understood from the following diagram. Let A B represent the 
surface of the ground prior to a glacial epoch, and to the for- 
mation of the beds of coal and stratified deposits represented in 



CLIMATE AND TIME, 

the diagram. Let S 8* be the m^nul an* 

level. Suppose the eccentricity of the sutli'i 
orbit begins to increase, and the vintN Bcdatioe 
Approaches the perihelion, we have then a 
modemtely warm period. The sea-IevBl atnka 
to 1, and forests of sigillarise and other ooal 
trees cover the country from the sea-shore at 

1, strotching away inland in the direction of 
B. In course of time the winter solstice 
mo^'es round to aphelion and a cold period 
follows. The sea begins to rise and oontinnea 
rising till it reaches 1'. Denudation and the 
severity of the climate destroy every vestige 
of tho forest from 1' backwards into the in- 
terior ; but the portion 1 l' being submerged 
and covered over by sediment brought down 
from tho land is preserved. The eccentricity 
continuing to increase in extent, the second 
inter-glaciul period is more warm and equable 
than the first, and the sea this time sinks to 

2. A second forest now covers the country 
down to the sea-shoro at 3. This second warm 
period is followed by the second cold period, 
more severe than tho first, and the sea-level 
rises to 2', Denudation and seventv of climate 
now destroy every remnant of the forest, from 
2' inland, but of course the submerged portion 
of 2 2*, like the former portion 1 1', is pre- 
served. During the third warm period (the 
eccentricity being still on the increase) the 
sea-lcTel sinks to 3, and the country for the 
third timo is oovored by forests, which extend 
down to 3. This third warm period is fol- 
lowed by a cold glacial period more severe 
than the preceding, and the sea-level rises to 
3', and the snhmerged portion of the forest 



COAL AN INTER' GLACIAL FORMATION. 427 

from 3 to 3' becomes covered with drift, — the rest as before 
being destroyed by denudation and the severity of the climate. 
We shall assume that the eccentricity has now reached a 
maximum, and that during the fourth inter-glacial period the 
sea-level sinks only to 4, the level to which it sank during the 
second inter-glaciul period. The country is now covered for 
the fourth time by forests. The cold period which succeeds 
not being so severe as the last, the sea rises only to 4', which, 
of course, marks the limit of the fourth forest. The eccentricity 
continuing to diminish, the fifth forest is only submerged up 
to 5', and the sixth and last one up to 6'. The epoch of cold 
and warm periods being now at a close, the sea-level remains 
stationary at its old normal position 8 S'. Here we have six 
buried forests, the one above the other, which, through course 
of ages, become transformed into coal-beds. 

It does, not, however, necessarily follow that each separate 
coal-seam represents a warm period. It is quite possible that 
two or more seams separated from each other by thin partings 
or a few feet of sedimentary strata might have been formed 
during one warm period ; for during a warm period minor 
oscillations of sea-level sufficient to submerge the land to some 
depth might quite readily have taken place from the melting 
of polar ice, as was shown in the chapter on Submergence. 

It may be noticed that in order to make the section more 
distinct, its thickness has been greatly exaggerated. It will 
also be observed that beds 4, 5, and 6 extend considerably to 
the left of what is represented in the section. 

15 ut it is not to be supposed that the whole phenomena of the 
coal-fields can be explained without supposing a subsidence of 
the land. The great depth to which the coal-beds have been 
sunk, in many cases, must be attributed to a subsidence of the 
lovel. A series of beds formed during a glacial epoch, may, 
owing to a subsidence of the land, be sunk to a great depth, 
and become covered over with thousands of feet of sediment ; 
and then on the occurrence of another glacial epoch, a new 
series of coal-beds may be formed on the surface. Thus the 



^8 CLIMATE AND TIME. 

upper aeries may be separated from the lowar by ihovaands «f 
feet of sedimentary rock. There is another oonaeqaeiioe vesolt- 
ing from the sinking of the land, which must be taken into 
account. Had there been no sinking of the land doxing ibe 
Carboniferous age, the quantity of coal-beds now remaining 
would be far less than it actually is, for it is in a great measure 
owing to their being sunk to a great depth that they hare 
escaped destruction by the enormous amount of denudation 
which has taken place since that remote age. It therefore fol« 
lows that only a very small fraction of the submerged forests 
of the Goal period do actually now exist in the form of coal. 
Generally it would only be those areas which happened to be 
sunk to a considerable depth, by a subsidence of the land, that 
would escape destruction from denudation. But no doubt the 
areas which would thus bo preserved bear but a small propor- 
tion to those destroyed. 

Length of Inter-glacial Period ^ as indicated by the Thickness of a 
Bed of Coal. — ^A fact favourable to the idea that the coal-seams 
were formed during inter-glacial periods is, that the length of 
those periods agrees pretty closely with the length of time sup-, 
posed to be required to form a coal-seam of average thickness. 
Other things being equal, the thickness of a coal-seam would 
depend upon the length of the inter-glaciul period. If the rate 
of precession and motion of the perihelion were always uniform 
the periods would all be of equal length. But although the 
rate of precession is not subject to much variation, such is not 
the case in regard to the motion of the perihelion, as will be 
seen from the tables of the longitude of the perihelion given in 
Chapter XIX. Sometimes the motion of the perihelion is 
rapid, at other times slow, while in some cases its motion is 
retrograde. In consequence of this, an intcr-glacial period 
may not be more than some six or seven thousand years in 
length, while in other cases its length may be as much as fifteen 
or sixteen thousand years. 

According to Boussingault, luxuriant vegetation at the pre-^ 
ly takes from the atmosphere about a half ton of carbon 



^jl^ay 



COAL AN INTER'GLACIAL FORMATION. 420 

per acre annually, or fifty tons per acre in a century. Fifty 
tons of carbon of the specific gravity of coal, about 1'6, spread 
evenly over the surface of an acre, would make a layer nearly 
one-third of an inch.* Humboldt makes the estimate a little 
higher, viz., one half- inch. Taking the latter estimate, it 
would require 7,200 years to form a bed of coal a yard thick. 
Dr. Heer, of Zurich, thinks that it would not require more than 
1,400 years to form a bed of coal one yard thick ;t while 
Mr. Maclaren thinks that a bed of coal one yard thick would 
be formed in 1,000 years. + Professor PhiUip, calculating 
from the amount of carbon taken from the atmosphere, aa 
determined by Liebig, considers that if it were converted into 
ordinary coal with about 75 per cent, of carbon, it would yield 
one inch in 127*5 years, or a yard in 4,600 years. § 

There is here a considerable amount of diflerence in regard 
to the time required to form a yard of coal. The truth, how- 
ever, may probably be somewhere between the two extremes, 
and we may assume 5,000 years to be about the time. In a 
warm period of 15,000 years we should then have deposited a 
setim of coal 9 feet thick, while during a warm period of 
7,000 years we would have a seam of only 4 feet. 

Reason why the Coal Strata present so little Evidence of Ice- 
action. — There are two objections which will, no doubt, present 
themselves to the reader's mind. (1.) If coal be an inter- 
glacial formation, why do the coal strata present so little 
evidence of ice-action ? If the coal-seams represent warm 
inter-glacial periods, the intervening beds must represent cold 
or glacial periods, and if so, they ought to contain more abundant 
evidence of ice-action than they really do. (2.) In the case of 
the glacial epoch, almost every vestige of the vegetation of tho 
warm periods was destroyed by the ice of the cold periods ; 
why then did not the same thing take place during the glacial 
epoch of the Cjirboniferous period ? 

♦ See "Smithsonian Keport for 1857," p. 138. 
f (iuart. Joum. Geol. Soc., May, 1866, p. civ. 
\ *♦ Geology of Fife and the ly.thians," p. 116. 
9 " Life on the Earth." p. 133. 




f30 CLIMATE AND TIME. 

During tho gLicial epoch the face of the countiy was in all 
pnjbubility covered for ages with the most luxariant yegetatioii; 
but scarcely a vestige of that vegetation now Temains, indeed 
the very soil upon which it grew is not to be found. All that 
now remains is the wreck and desolation produced by the ioe- 
shcct that covered the country during the cold periods of that 
(^poch, couHiHting of transported blocks of stones, polished and 
grooved rocks, and a confused mass of boulder clay. Here we 
liave in this epoch nothing tangible presenting itself but the 
destructive oflects of the ice which swept over the land. Why, 
then, in reference to the glacial epochs of the Carboniferous 
age should we have such abundant evidence of the vegetation 
of the warm periods, and yet so little evidence of the effect of 
tho ice of tho cold periods P The answer to these two objection3 
will go a gnvit way to explain why we have so much coal 
bclonginji; to tlio Carbon iforous age, and so little belonging to 
any oth(T ii<^c ; and it will, I think, be found in the peculiar 
physical clianicter of tlio country during the Carboniferous 
ugo. The areas on which the forests of the Coal period grew 
escaiHjd tho d instructive power of glaciers and land-ice on 
account of tho flat nature of the ground. There are few 
points on which geologists are more unanimous than in rcgarf 
to tho flat character of the country during the Coal period. 

There does not seem to bo any very satisfactory evidence 
tliat tlio interior of the country rose to any very great elevation. 
31 r. Godwin-Aufiten thinks that during the Coal period there 
must have been " a vast expanse of continuous horizontiil sur- 
face at very slight elevations above the sea-level." • Of the 
widely spread terrestrial surface of the Coal-nieasuro period, 
portions, he believes, attained a considerable elevation. But in 
contrast to this he states, ** There is a feature which seems to 
distinguish this pt^riod physically from all subsequent periods, 
and which cou.^ists in the vast expanse of continuous hori- 
zuutul surface which the laud area presented, bordering on, 
und at very slight elevations above, the sea-level." f Hugli 

Unart. Journ. Geol. Soc., vol. xi., p. 635. f Ibid., vol. xii., p. 39. 



COAL AN INTER-GLACIAL FORMATION. 431 

Miller, describing in his usual graphic way the appearance of 
the country during the Coal period, says : — " It seems to have 
been a land consisting of immense flats, unvaried, mayhap, by 
a single hilly in which dreary swamps, inhabited by doleful 
creatures, spread out on every hand for hundreds and thousands 
of miles ; and a gigantic and monstrous vegetation formed, as I 
have shown, the only prominent features of the scenery." * 

Now, if this is in any way like a just representation of the 
general features of the country during the Coal period, it was 
pliysically impossible, no matter however severe the climate 
may have been, that there could have been in this country at 
that period anything approaching to continental ice, or perhaps 
even to glaciers of such dimensions as would reach down to 
near the sea-level, where the coal vegetation now preserved is 
supposed chiefly to have grown. The condition of things which 
would prevail would more probably resemble that of Siberia 
than that of Greenland. 

The absence of all traces of ice-action in the strata of the 
coal- measures can in this case be easily explained. For as by 
supposition there were no glaciers, there could have been no 
scratching, grooving, or polishing of the rocks ; neither could 
there have been any icebergs, for the large masses known as 
icebergs are the terminal portions of glaciers which have reached 
down to the sea. Again, there being no icebergs, there of 
course could have been no grinding or scratching of the rocks 
forming the floor of the ocean. True, during summer, when 
the frozen sea broke up, we should then have immense masses 
of floating ice, but these masses would not be of suflBcient thick- 
ness to rub agiiinet the sea-bottom. But even supposing that 
they did occasionally touch the bottom here and there, we could 
not possibly fijid the evidence of this in any of the strata of the 
coal-measures. We could not expect to find any scratchings 
or markings on the sandstone or shale of those strata indicating 
the action of ice, for at that period there were no beds of sand- 
stone or shale, but simply beds of sand and mud, which in 

• Miller's '< Sketch Book of Practical Geology,'* p. 192. 



fjs CLIMATE AND TIME. 

fnture ngcA Lccamo consolidated into sandstone and shale. A 
maflfl of ico might occiisionally rub along the sea-bottom, and 
Ifiave itH markings on tlic loaso sand or soft mud forming that 
lK)tf,om, but the iioxt wave that passed over it would obliterate 
every mark, and l(*uvc tlio surface as smooth as before. Neither 
could we exiHM-t to iind any large erratics or boulders in the 
cotd stmta, for these must come frum the land, and as by suppo- 
sition tliere were no glaciers or land-ice at that period, there 
was th(Tcforc no moans of transporting them. In Greenland 
the ic<^l)org8 Homctimes carry large boulders, which are dropped 
into the S(*a as the icebergs melt away ; but these blocks haye 
all either been transported ou the backs of glaciers from inland 
tracts, or have fallen on the field-ice along the shore from the 
face of crags and overhanging precipices. But as there were 
probably indth'^r glaciers reaching to the sea, nor perhaps pre- 
cipitous el ills along tlie sea-short*, there could have been few or 
no blocks tran-i)orted by ico and dropped into the sea of the 
Carboniferous period, and of course wc need not expect to find 
thetn in the sandstone and shale which during that eixxih formed 
the bed of the ocean. There would no doubt be coast-line ice 
and ground-i(*e in rivers, carrying away large quantities of 
gravel and stones ; but these gravels and stones would of course 
be all wat<T-worn, and altliou;j!:Ii found in the strata of the coal- 
measures, as no doubt they actually are, they would not be 
regarded as indicating the action of ice. The simple absence of 
relics of ic(?-action in the coil-measures proves nothing what- 
ever in regard to whether there were cold periods during their 
formation or not. 

This comparative absence of continental ice might be one 
re:is(m why the forests of the Carboniferous period have been 
preserved to a much greater extent than those of any other age. 

It must be observed, however, that the conclusions at which 
wo have arrived in reference to the comparative absence of con- 
tinental ice a]>plies only to the areas which now constitute our 
coa l-fields. The accumulation of ice on the antiirctic regions, 
^INkpi some parts of the arctic regions, might have been as 



COAL AN INTER-GLACIAL FORMATION. 433 

great during that age as it is at present. Had there been no 
continental ice there coidd have been no such oscillations of 
sea-level as is assumed in the foregoing theory. The leading 
idea of the theory, expressed in a few words, is, that the glacial 
epochs of the Carboniferous age wore as severe, and the accumu- 
lation of ice as great, as during any other age, only there were 
large tracts of flat country, but Kttle elevated above the sea- 
Icvcl, which were not covered by ice. These plains, during the 
warm inter-glacial periods, were covered with forests of sigil- 
laria) and other coal trees. Portions of those forests were pro- 
tected by the submergence which resulted from the rise of the 
sea- level during the cold or glacial periods and the subsequent 
subsidence of the land. Those portions now constitute our coal- 
beds. 

But that coal may be an inter-glacial formation is no mere 
hypothesis, for we have in the well-known Diimten beds 
— described in Chapter XV. — an actual example of such a 
formation. 

Carboniferous Limestones. — As a general rule the limestones 
of the Carboniferous period, like the coal, are found in beds 
separated by masses of sandstone and other stratified deposits, 
which proves that the corals, crinoids, and other creatures, of 
the remains of which it is composed, did not live continuously 
on during the entire Limestone period. These limestones are a 
marine formation. If the land was repeatedly submerged the 
coal must of necessity have been produced in seams with stratified 
deposits between, but there is no reason why the same should 
htive been the case with the limestones. If the climatic condi- 
tiun of the sea continued the same we should not have expected 
this alternate succession of life and death ; but, according to the 
theory of alternate cold and warm periods, such a condition 
follows as a necessary consequence, for during the warm periods, 
when the land was covered with a luxuriant vegetation, the sea- 
bottom would be covered with moUusca, crinoids, corals, &c., 
fitted to live only in a moderately warm sea; but when the 
oold came on those creatures would die, and their remains. 



V 






f34 CLIMATE AND TIME, 

during iho continuance of tho cold period, would become sic 
covered over with deposits of sand and clay. On the retur 
the warm period those deposits would soon become coTered i 
life as before, forming another bed of limestone, and this a] 
nation of life and death would go on as long as the gli 
epoch continued. 
5 It is true that in Derbyshire, and in the south of Ireland 

some other places, the limestone is found in one mass of sev 
hundred feet in thickness without any beds of sandstone 
shale, but then it is nowhere foimd in one continuous i 
I* , from top to bottom without any lines of division. These bn 

or divisions may as distinctly mark a cold period as though 1 
had been occupied by beds of sandstone. The marine creat 
ceased to exist, and when tho rough surface left by t 
remains became smoothed down by the action of the wi 
into a flat plain, another bed would begin to form upon 
floor so soon as life again appeared. Two agencies worl 
together probably conspired to produce these enormous ma 
of limestone divided only by breaks marking diflTerent per 
of elaboration. Corals grow in warm seas, and there onlj 
water of a depth ranging from 20 to 30 fathoms. The cole 
a period of glaciation would not only serve to destroy th 
but they would be submerged so much beyond the depth pn 
for their existence that even were it possible that with 
submergence a sufficient temperature was left, they w( 
inevitably perish from the superincumbent mass of water, 
are therefore, as it seems to me, warranted in concluding 1 
the separate masses of Derbyshire limestone were formed dui 
warm inter-glacial periods, and that the lines of division re] 
sent cold periods of glaciation during which the animals peris 
by the combined influence of cold and pressure of water. ' 
submergence of the coral banks in deep water on a sea-bott 
which, liko the land, was characteristically flat and even, imj 
its carrying away far into tho bosom of the ocean, and co 
qaeq||BMBpte from any continent and the river-borne detz 




qa0D||attHV)t 



CHAPTER XXVII. 

PATH OF THE ICE-SHEET IN NORTH-WESTERN EUROPE AND ITS 
RELATIONS TO THE BOULDER CLAY OF CAITHNESS.* 

Character of Caithness Boulder Clay. — ^Theories of the Origin of the Caithnesa 
Clay. — Mr. Jamieson's Theory. — Mr.C. W. Peach's Theory. — The proposed 
Theory. — ThicknoMS of Scottish Ice-sheet. — Peatlands striated on their 
Summits. — Scanilinavinn Ice-sheet. — North Sea filled with Land-ice. — Gretit 
Baltic Glacier. — Jutland and Denmark crossed hy Ice. — Sir R. Murchison's 
Observations. — Orkney, Shetland, and Faroe Islands striated across. — 
Loess accounted for. — Professor Ueikie's Sugujestion. — Professor Geikie and 
B. N. Pouch's OWs'Tvutions on East Coast of Caiiiiness. — Evidence from 
Chulk Plints and Ouliiic Fossils in Boulder Clay. 

The Nature of the Caithness Boulder Clay, — A considerable 
amount of difficulty has been felt by geologists in accounting 
for the origin of the boulder clay of Caithness. It is an iin- 
fitratified clay, of a deep grey or slaty colour, resembling much 
that of the Caithness flags on which it rests. It is thus de< 
scribed by Mr. Jamieson (Quart. Jour. Geol. Soc, vol. xxii., 
p. 261) :— 

" The glacial drift of Caithness is particidarly interesting as 
an example of a boulder clay which in its mode of accumulation 
and ice-scratched debris very much resembles that unstratified 
stony mud which occurs underneath glaciers — ^the 'moraine 
profomhy as some call it. . 

" The appearance of the drift along the Haster Bum, and in 
many other places in Caithness, is in fact precisely the same as 
that of the old boulder clay of the rest of Scotland, except 
that it is charged with remains of sea-shells and other marine 
organisms. 

• From Geolog^ical 3Iag;izine^ May and June, 1870 ; with a few yerbal coirec- 
tiouH, and u 8lip:ht ve-arr.mgiment ot the paragraphs. 



«6 CLIMATE AND TIME, 

** If want of stratification, hardness of texture, and abonda 
of well-glaciated stones and boulders are to be the tests 
what we call genuine boulder clay, then much of the Caithn 
drift will stand the ordeal." 

So far, therefore, as the mere appearance of the drift 
concerned, it would at once be pronounced to be true Lo^ 
Till, the product of land-ice. But there are two circumstan 
connected with it which have been generally regarded as fa 
to this conclusion. 

(1) The striflo on the rocks show that the ice which forn 
the clay must have come from the sea, and not from 1 
interior of the country ; for their direction is almost at ri{ 
angles to what it would have been had the ice come from 1 
interior. Over the whole district, the direction of the groo' 
and scratches, not only of the rocks but even of the stones 
the clay, is pretty nearly N.W. and S.E. ** When examini 
the sections along the Ilaster Burn," says Mr. Jamieson, ** 
company with Mr. Joseph Anderson, I remarked that the sti 
on the imbedded fragments gc^nerally agreed in direction w: 
those of the rocks beneath. The scratches on the boulders, 
usual, run lengthways along the stones when they are of 
elongated form ; and the position of these stones, as they 
imbedded in the drift, is, as a rule, such that their longer a: 
point in the same direction as do the scratches on the solid re 
beneath ; showing that the same agency that scored the rot 
also ground and pushed along the drift." 

Mr. C. W. Peach informs me that he seldom or never fou 
a stone with two sots of strife on it, a fact indicating, as ^ 
Jamieson remarks, that the drift was produced by one gr< 
movement invariably in the same direction. Let it be boi 
in mind that the ice, which thus moved over Caithness in tl 
invariable track, must either have come from the Atlantic 
the N.W., or from the Moray Firth to the S.E. 

(2) The boulder clay of Caithness is full of sea-shells a 
other marine remains. The shells are in a broken conditi< 
and are interspersed like the stones through the entire mass 



H^ri 



ICE'SHEET IN NORTH-WESTERN EUROPE, 437 

the clay. Mr. Jamieson states that he nowhere observed any 
instance of shells being found in an imdisturbed condition, 
** nor could I hear," he says, " of any such having been found ; 
there seems to be no such thing as a bed of laminated silt with 
shells in sit 11.^* The shell-fragments are scratched and ice- 
worn, the stime as the stones found in the clay. Not only are 
the shells glaciated, but even the foraminifera, when seen 
through the microscope, have a rubbed and worn appearance. 
The shells have evidently been broken, striated, and pushed 
along by the ice at the time the boulder clay was being 
formed. 

Theories regarding the Origin of the Caithness Clay. — Mr. 
Jamieson, as we have seen, freely admits that the boulder clay 
of Caithness has the appearance of true land-ice till, but from 
the N.W. and S.E. direction of the strice on the rocks, and the 
presence of sea-sheUs in the clay, he has come to the conclusion 
that the glaciation of Caithness has been effected by floating 
ice at a time when the district was submerged. I have alway 
felt convinced that Mr. Jamieson had not hit upon the true 
explanation of the phenomena. 

(1) It is physically impossible that any deposit formed by 
icebergs could be wholly unstratified. Suppose a mass of the 
materials which would form boulder clay is dropped into the 
sea from, say an iceberg, the heavier parts, such as stones, will 
reach the bottom first. Then will follow lighter materials, 
such as sand, then clay, and last of all the mud will settle down 
over the whole in fine layers. The different masses dropped 
from the various icebergs, will, no doubt, lie in confusion one 
over the other, but each separate mass will show signs of 
stratification. A good deal of boulder clay evidently has been 
formed in the sea, but if the clay be unstratified, it must have 
been formed under glaciers moving along the sea-bottom as on 
dry ground. Whether unstratified boulder clay may happen 
to be formed under water or on dry land, it must in either case 
be the product of land- ice.* Those who imagine that materials, 

• See Phil. Mag. for November, 1868, p. 374. 



4jf CUMATE AND TIME. 

difiering in specific gravity like tlioae wluoh. con n w e booldiv 
clay, dropped into water, can settle down williovl ■flmming llie 
stratified form, should make the experiment^ and thsj would 
soon satisfy themselves that the thing is pkysicallj imp os Mb lft 
The notion that unstratified boulder day coold be fiarmed by 
deposits from floating ice, is not only erroneous, but positirely 
pernicious, for it tends to lead those who entertain it astray in 
regard to the whole question of the origin of drift. 

(2) It is also physically impossible that ice-markings^ sock 
as those everywhere found on the rocky fiioe of the district^ 
and on the pebbles and shells imbedded in the day, could have 
been cfiectcd by any other agency than that of land-ice. I 
need not here enter into any discussion on this point, as this 
bus bc^3n done at considerable length in another place.* 
Ju the present cjise, however, it is unnecessary, because if it 
can b(; shown that all the facta are accoimted for in the most 
natural manner by the theory of land-ice, no one will contend 
for the floating-ice theory ; for it is admitted that, with the 
exception of the direction of the striae and the presence oi the 
shellfl, all the facts agree better with the Lxnd-ice than with the 
floating-ice theory. 

My first impression on the subject was that the glaciation of 
CaithncHS had been effected by the polar ice-cap, which, during 
the Hcver<T part of the glacial epoch, must have extended down 
to at least the latitude of the north of Scotland. 

Oi> a fornujr occasion (see the Reader for 14th October, 
18f)/}) it was shown that all the northern seas, owing to their 
shallowness, must, at that period, have been blocked up with 
solid ice, wliich displaced the water and moved along the sea- 
bottoms the same as on dry land. In fact, the northern seas, 
including the German Ocean, being filled at the time with 
glacier-ice, might be regarded as dry land. Ice of this sort, 
moving along the bed of the German Ocean or North Sea, and 
over Caithness, could not fail to push before it the shells and 
other animal remains lying on the sea-bottom, and to mix 

• Soo Phil. Mag. for November, 1868, pp. 306—374. 




ICX-SHEET IN NORTH- WESTERN EUROPE 4jq 

thoni up with the day which now remains upon the land aa 
evidence of its progress. 

About two years ago I had a conversation with Mr. C. W. 
Peach on the subject. This gentleman, as is well known, has 
long been fitmiliar with the boulder day of Caithness. He felt 
convinced that the clay of that country is the true Lower Till, 
and not a more recent deposit, as Mr. Jamieson supposes. He 
expressed to me his opinion that the glaciation of Caithness 
had been effected by masses of land-ice crossing the Moray 
Firth from the mountain ranges to the south-east, and passing 
over Caithness in its course. The difficulty which seems to 
beset this theory is, that a glader entering the Firth would 
not leave it and ascend over the Caithness coast. It would 
take the path of least resistance and move into the North Sea, 
where it would find a firee passage into deeper water. Mr. 
Peach's theory is, however, an important step in the right 
direction. It is a part of the truth, but I believe not the whole 
truth. The following is submitted as a solution of the question. 

The Proposed Theory. — ^It may now be regarded as an es- 
tablished &ct that, during the severer part of the glacial 
period, Scotland was covered with one continuous mantle of 
ice, so thick as to bury under it the Ochil, Sidlaw, Pendand, 
Campsie, and other moderatdy high mountain ranges. For 
example, Mr. J. Oeikie and Mr. B. N. Peach found that the 
great masses of the ice firom the North-west Highlands, (»une 
straight over the Ochils of Perthshire and the Lomonds of Fifeu 
In fact, these mountain ridges were not sufficiently high to deflect 
the icy sti'eam either to the right hand or to the left ; and the 
flattened and rounded tops of the Campsie, Pentland, and 
Lammermoor ranges bear ample testimony to the denuding 
power of ice. 

Further, to quote from Mr. Jamieson, ''the detached moun- 
tain of Schohallion in Perthshire, 3,500 feet high, is marked 
near the top as well as on its flanks, and this not by ice flowing 
down the sides of the hill itself but by ice pressing over it 
from the north. On the top of another isolated hill^ called 

20 



MO 



CLIMATE AND TIME. 



I 






Morven, about 3,000 feet higli, and ntnated a hm miles tD 
north of the village of Ballater, in the ooonty of Aberdea 
found granite boulders unlike the rock of the hill, and ap 
rently derived from the mountains to the west. Again, <m 
highest water-sheds of the Ochils, at altitudes of about 2y< 
feet, I found this summer (1864) pieces of mica schist fuD 
garnets, which seem to have come from the Ghrampian HQl 
the north-west, showing that the transporting agent bad 01 
flowed even the highest parts of the Ochil ridge. And on 
West Lomonds, in Fifoshire, at Clattering-well Qnany, 1/ 
feet high, I found ice-worn pebbles of Bed Sandstone \ 
porphyry in the dihri% covering the Carboniferous liimest 
of the top of the Bishop Hill. Facts like these meet us ere 
where. Thus on the Perthshire Hills, between Blair At 
and Dunkeld, I foiind ice-worn surfaces of rocks on the top 
hills, at elevations of 2,200 feet, as if caused by ice press 
over them from the north-west, and transporting boulders 
even greater heights." * 

Facts still more important, however, in their bearing on 
question before us were observed on the Pentland range by ] 
Bennie and myself during the summer of 1870. On ascendi 
Allermuir, one of the hills forming the northern termination 
the Pentland range, we were not a little surprised to find 
summit ice-worn and striated. The top of the hill is compo 
of a compact porphyritic felstone, which is very much brol 
up ; but wherever any remains of the original surface could 
seen, it was foimd to be polished and striated in a most decic 
manner. These striae are all in one uniform direction, nea 
east and west ; and on minutely examining them with a I 
we had no difficidty whatever in determining that the 
which effected them came from the west and not from the ei 
a fact which clearly shows that they must have been made 
the time when, as is well known, the entire Midland valley 1 
filled with ice, coming from the North-west Highlands, 
the summit of the hill we also found patches of boulder clay 

♦ Joam. Geol. Soo., toI. xxi., p. 165. 



ICE' SHEET IN NORTH-WESTERN EUROPE. 44.1 

hollow basins of the rock. At one spot it was upwards of a 
foot in depth, and rested on the ioe-polished surfiEtoe. The 
clay was somewhat loose and sandy, as might be expected of a 
layer so thin, exposed to rain, frost, and snow, during the long 
course of ages which must have elapsed since it was deposited 
there. Of 100 pebbles collected firom the clay, just as they 
turned up, eyery one, with the exception of three or four 
composed of hard quartz, presented a flattened and ice-worn 
surface; and forty-four were distinctly striated: in short, 
every stone which was capable of receiving and retaining 
scratches was striated. A number of these stones mxurt have 
come from the Highlands to the north-west* 

The height of AUermuir is 1,617 feet, and, from its position, 
it is impossible that the ice oould have gone over its summit, 
unless the entire Midland valley, at this place, had been filled 
with ice to the depth of more than 1,600 feet. The hill is 
situated about four or five miles to the south of Edinburgh, 
and forms, as has already been stated, the northern termination 
of the Pentland range. Immediately to the north lies the 
broad valley of the Firth of Forth, more than twelve miles 
across, offering a most £ree and unobstructed outlet for the 
great mass of ice coming along the Midland valley from the 
west. Now, when we reflect how easily ice can accommodate 
itself to the inequalities of the channel along which it moves, 
how it can turn to the right hand or to the left, so as to find 
for itself the path of least resistance, it becomes obvious that 
the ice never would have gone over Allermuir, unless not only 
the Midland valley at this point, but also the whole sur- 
rounding country had been covered with one continuous mass 
of ice to a depth of more than 1,600 feet. But it must not be 
su])po8ed that the height of Allermuir represents the thickness 
of the ice ; for on ascending Scald Law, a hill four miles to the 
south-west of Allermuir, and the highest of the Pentland 
range, we found, in the tUbru covering its summit, hundreds 

* Specimens of tlie striRted summit and boulder clay Btsnm are to be Men ill 
the EdmbaTgh Museam of Sdeoce and Art. 



141 CLIMATE AND TIME. 

tif tr«ftiiM|Hiriiid nUmon of all inztiBt from one to 
in diiiinnUir. Wo oImo dug up a Oreentlona hoaMrr 
Iii^lif4i4iti itii'JiiM ill diiifnoiiT, which was finely pnJMW 
NirUUtil. A« ilio hniKhi of thi» hiU is 1,898 fiw^ lb* mm if 
iiw «M»v(trliig ilin Nurroundiiig country murt hsTe faeea at IcMi 
l,tlO() fiMii diu«p. liut UiiN iH not all. Directly to lb* nottk «f 
IliM I'tMillutMU, ill li lliio iiuiirly parallel with the eut ooul^ and 
at i'IkIiI liiiKhm to ili» jNith of ioe from the interior^ theve ia no^ 
wiUi ilin i«»iM«|)iioit of ihu Noliiary peak of East Lonumdl, and a 
low lilU or two ttt Urn Hidlaw rungo, an eminence worthy of the 
imiiiM of a liill iiiuiror ihun the Grampians in the north of 
T'oi'lurpiliirn. iliMiuiii upwanU of Hixty miles. This broad plaiop 
i»Kt4iiMliiif( rrotti iilitumt ttiu Houthern to the Northern HigUandi^ 
Witrt tlin fj!;riiiil. rliiitiMol lliruu^li which the ice of the interior of 
Hi'mIIiumI rmitifl (111 oiillrl. into tlio North Sea. If the depth of 
tliM irn ill llin l*'irtli of l^'ortli, which forms the southern side of 
(IiIm lirniiil linltiiw, wiiN III hmHt 1,000 feet, it is not at all 
priilHililM tliiil. i(N ilt'pih in the norlbern side, formed by the 
Vitllity of •Slnithiiiorn iind the Firth of Tuy, which lay more 
iliriuilly ill \\\o piilli of tlut ire from the North Highlands, could 
imvo Imm'Ii IrNN. Ilrre wo have one vast glacier, more than 
9k\\\\ itiiltm liroitd ttiul I,1M)() IW^t thick, coming from the interior 
of tliit roiiiitrv. 

It IN, thontlnns rvidont that the great mass of ice entering 
tho North S(Mi to tho iminI of SiH>thnul, especially about the 
I*'irtliH o( VnviU and Tay. conUl not have been less, and was 
|)rohu)>ly iinii'h nutiv, than iVom 1,000 to 2,000 feet in thick- 
noNN. 'i'ho grand (]urMtion now to be considered is, What 
lHM*iini(« of tho lingo nhrrt »)f ioo aflt^r it entered the North Sea? 
Dill it ItrtMik np and tloiit away as icebergs? This appears to 
havi« lu*en bithtM'to taken for granted ; but the shallowness of 
tht» North Si'a nbows sueh u process to have been utterly im- 
IMHHible. The depth of the sea in the English Channel is only 
alMuit twenty fathoms, and although it graduidly increases to 
about forty fathoms at the Moray Firth, yet we must go to the 
fl^i^kimd west of the Orknev and Shetland Islands ere we 



ICE' SHEET IN NORTH- WESTERN EUROPE 44S 

reach the 100 fathom line, ^ub the ayerage deptti of the 
entire North Sea is not oyer forty fathoms, which is even in* 
BTifficient to float an iceberg 300 feet thick. 

No doubt the North Sea, for two reasons^ is now mnch 
shallower than it was during the period in question. (1.) 
There would, at the time of the great extension of the ioe on 
the northern hemisphere} be a considerable submergence, result- 
ing from the displacement of the earth's centre of gravity.* 
(2.) The sea-bed is now probably filled up to a larger extent 
with drift deposits than it was at the ioe period. But, after 
making the most extravagant allowance for the additional depth 
gained on this account, still there could not possibly have been 
water sufficiently deep to float a glacier of 1,000 or 2,000 feet 
in thickness. Indeed, the North Sea would have required to 
be nearly ten times deeper than it is at present to have floated 
the ice of the glacial period. We may, therefore, conclude with 
the most perfect certainty that the ice-sheet of Scotland could 
not possibly have broken up into icebergs in such a channel, 
but must have moved along on the bed of the sea in one un- 
broken mass, and must have found its way to the deep trough 
of the Atlantic, west of the Orkney and Shetland Islands, ere 
it broke up and floated away in the iceberg form. 

It is hardly necessaiy to temork that the waters of the 
North Sea would have but little effect in melting the ice. A 
shallow sea like this, into which large masses of ice were 
entering, would be kept constantly about the freezing-point» 
and water of this temperature has but little meltiDg power, 
for it takes 142 lbs. of water, at 33^, to melt one pound of ice. 
In fact, an icy sea tends rather to protect the ice entering it 
from being melted than otherwise. And besides, owing to 
fresh acquisitions of snow, the ice*sheet would be accumulating 
more rapidly upon its upper sur&ee than it would be melting at 
its lower surfieu^e, supposing there were sea-water under that 
surface. The ice of Scotland during the glacial period must^ 
of necessity, have found its way into warmer water than that of 

• Fhfl. Hag. for April, 186ft. 



i 



1 



i44 CLIMATE AND TIME. 

the North Sea before it could have been melted. But i 
could not do without reaching the Atlantic, and in ge 
there it Tould have to puss round by the Orkney Isl 
along the bed of the North Sea, as land-ice. 

This will explain how the Orkney iBlunds may have 
glaciated by land-ico ; but it does not, however, explain 
Caithness should have been glaciated by that means. ^ 
islands lay in the very track of the ice on its way t< 
Atlantic, and could hardly escape being overridden; 
Caithncfis lay considerably to the left of the path whie 
should expect the ice te have taken. The ice would not 
its channel, turn to the left, and ascend upon Caithness, n 
it were forced to do so. AVhat, then, compelled the ice to 
over CaithneBs P 

I'ath of the SraiuUiuirian Ice. — ^Vc must consider Ibut tl 
from Scotland and England was but a fnicfion of that v 
entei'od the North Sea. Tlie greater part of the ic 
Scandinavia must liave gone into this sea, and if the ice o. 
ii>laud could not tiud water sufGciently deep in which to 
far less would the much thicker ice of Scandinavia do so. 
Scandinavian iuo, before it could break up, would thus, lik 
Scottish ice, have to cross the bed of the North Sea and 
into tlio Atlautic. It could not pass to the north, or to 
north-west, far the oce:in in these directions would be blc 
up by tho polar ice. It is true that along the southern i 
of Norway there osfends a comparativoly deep trough of 
one to tno hundred fathoms. But this is evidently not 
enough to havo floated tho Scandinavian ice-sheet; and 
supposing it had been sufficiently deep, the floating ice must 
found its way to the Atlantic, and this it could not have 
without passing along the coast. Now, its passage wouli 
only be obstructed by the mass of ice continually protru 
into the sea directly at right angles to its course, but it v 
be met by the still more enormous masses of ice comin 
the entire Norwegian coast-lino. And, besides this, th 
entering the Arctic Ocean from Lapland and the nort 



ICE'SHEET IN NORTH- WESTERN EUROPE. 445 

parts of Siberia, except the very small portion which might 
find an outlet into the Pacific through Behring's Straits, 
would have to pass along the Scandinavian coast in its way to 
the Atlantic. No matter, then, what the depth of this trough 
may have been, if the ice from the land, after entering it, could 
not make its escape, it would continue to accumidato till the 
trough became blocked up ; and after this, the great mass 
from the land would move forward as though the trough had 
no existence. Thus, the only path for the ice would be by the 
Orkney and Shetland Islands. Its more direct and natural 
path would, no doubt, be to the south-west, in* the direction of 
our shores ; and in all probability, had Scotland been a low flat 
island, instead of being a high and mountainous one, the ice 
would have passed completely over it. But its mountainous 
character, and the enormous masses of ice at the time pro- 
ceeding from its interior, would efiectually prevent this, so 
that the ice of Scandinavia would be compelled to move round 
by the Orkney Islands. Consequently, these two huge masses 
of moving ice — the one from Scotland and the much greater 
one from Scandinavia — ^would meet in the North Sea, probably 
not far from our shores, and would move, as represented in the 
diagram, side by side northwards into the Atlantic as one 
gigantic glacier. 

Nor can this be regarded as an anomalous state of things ; 
for in Greenland and the antarctic continent the ice does not 
break up into icebergs on reaching the ^ea, but moves along the 
sea-bottom in a continuous mass until it reaches water suffi- 
ciently deep to float it. It is quite possible that the ice at the 
present day may nowhere traverse a distance of three or four 
hundred miles of sea-bottom, but this is wholly owing to the 
fact that it finds water sufficiently deep to float it before having 
travelled so far. Were Baffin's Bay and Davis's Straits, for 
example, as shallow as the North Sea, the ice of Greenland 
would not break up into icebergs in these seas, but cross in one 
continuous mass to and over the American continent. 

The median line of the Scandinavian and Scottish ice- sheets 






i 



44* CLIMATE AND TTMK. 

would be situated not &r from the east oout of Snnft i aff A 
Soandinavioii ice would press up as near to our ooHt m fl 
resistanoe of the ice from this side permitted. Hie enonnoi 
mass of ice from Scotland, pressing out into the North Sea, wool 
oompcl the Scandinavian ice to move round by the OikiMji 
and would also keep it at some little distance from Sootlani 
Where, on the other hand, there was but little resnstaiioe ofiSnc 
by ice from the interior of this country (and this might be tli 
case along many parts of the English coast), the Soandinavia 
ice might reach the shores, and even overrun the country fi 
some distance inland. 

We have hitherto confined our attention to the action of if 
proceeding from Norway ; but if we now consider what too 
place in Sweden and the Baltic, we shall find more condusii 
I proof of the downward pressure of Scandinavian ice on our ow 

shores. The western half of Gothland is striated in the dura 
tion of N.E. and S.W., and that this has been efiTected by 
\ huge mass of ice covoriug the country, and not by lea 

^ glaciers, is apparent from the fact observed by Bobert Chan 

bers,* and oiHcors of the Swedish Geological Survey, that tl 
general direction of the groovings and strise on the rocks beai 
little or no relation to the conformation of the surface, showin 
that the ice was of sufficient thickness to move straight forwan 
\ regardless of the inequalities of the ground. 

|| At Gottonburg, on the shores of the Cattegat, and all aroun 

.' Luke Wener and Lake Wetter, the ice-markings are of tl 

w most remarkable character, indicating, in the most decide 

manner, that the ice came from the interior of the country 1 
the north-east in one vast muss. All this moss of ice must hai 
gone into the shallow Cattegat, a sea not sufficiently deep 1 
float even an ordinary glacier. The ice coming oflf Gothlaii 
would therefore cross the Cattegat, and thence pass over Ju 
land into the North Sea. After entering the North Sea, 
would be obliged to keep between our shores and the ice comic 
direct from the western side of Scandinavia. 



« ( 



'Tracings of the North of Europe," 1850, pp. 48—61. 



ICE- SHEET IN NORTH-WESTERN EUROPE. 447 

But this is not alL A verj large proportion of the Scandi- 
navian ice would pass into the Ghdf of Bothnia, where it could 
not possibly float. It would then move south into the Baltic 
as land-ice. After pasaing down the Baltic, a portion of the ice 
would probably move south into the flat plains in the north of 
Germany, but the greater portion would keep in the bed of the 
Baltic, and of course turn to the right round the south end of 
Gothland, and thence cross over Denmark into the North Sea. 
That this must have been the path of the ice is, I think, obvious 
from the observations of Murchison, Qiambers, Horbye, and 
other geologists. Sir Boderick Murchison found — ^though he 
does not attribute it to land- ice — ^that the Aland Islands, which 
lie between the Gxdf of Bothnia and the Baltic, are all striated 
in a north and south direction.* 

Upsala and Stockholm, a tract of flat country projecting for 
some distance into the Baltic, is also grooved and striated, not 
in the direction that would be effected by ice coming from the 
interior of Scandinavia, but north and south, in a direction 
parallel to what must have been the course of the ice moving 
down the Baltic, t This part of the country must have been 
striated by a mass of ice coming from the direction of the Ghdf 
of Bothnia. And that this mass must have been great is appa- 
rent from the fact that Lake Malar, which crosses the country 
from east to west, at right angles to the path of the ice, does 
not seem to have had any influence in deflecting the icy stream. 
That the ice came from the north and not from the south is 
also evident from the fSact that the northern sides of rocky 
eminences are polished, rounded, and ice-worn, while the 
southern sides are comparatively rough. The northern banks 
of Lake Malar, for example, which, of course, face the south, 
are rough, while the southern banks, which must have offered 
opposition to the advance of the ice, are smoothed and rounded 
in a most singular manner. 

* Quart Joum. G^l. Soo.. toI. ii., p. 364. 

t ** Tracings of the Noita of Einope," by BoT>ert Chambers, pp. 2iS9, 2S5. 
*< ObtervatioDB sur lee Phdnomtees d'Broiioii en NorTdge," by H. Horbye, 1S67* 
also Pkofeesor Erdmann'a *' Fonnsiioiif Qoatemairea de la Bukle." 



hs climate axd time. 

Ajzaln, tbat tbe ice, after pa»m^ down the Baltic, tar 
tfac: ri^^ht aloni; the southern end of GotUaad, is shown 1 
directi'^n of the striiG and ice-grooTinga obaerred on 
uland.^ aa Gothland, Oiand, and Bomholm. Sir R. Mar 
found that thi: i4und of Gothland is grooved and atria' 
one Miiifi)nn direction from X.E. to S.W. "Thcae groov 
KiyK Sir }{ork-rick, " ho perfectly resemble the fiutings and 
\\tiA\xi-A'A in the Alps by the actual movement of glacier 
neillier Sf. AgnFiyiz nor any one of his eupporters conld d« 
rlifTcrvnce." Ho concludes, however, that the markings 
not liavo been made by land-ice, because Gothland is no 
a low, fliit iHland in the middle of the Baltic, hat is "a< 
41)0 niilcs distant from any elevation to which the te 
ni'iiiiilain can bo applied." This, of course, is com 
ii){uiiiHt the liyiHjttK'siH that Gothland and the other isla 
till! Jtiillii! Cduld hiivchi'en glaciated by ordinary glacieri 
it in (|iiilii in harmony with the theory that the Gulf of Bi 
mill thii entire Italtic were filled with one continuous n 
Inid-ii'c, derived from the drainage of the greater p 
Swiilcn, l^iphuid, and Finland. In fact, the whole | 
jilii'iioini'na of ISciindinavia urc inexplicable on the hyp< 
of Iwal nhn-icra, 

Tliiit the Italtio was c nin] do tely filled hya niasa of ice n 
fii>ni tin- lun'lli ifi further evidenced by the fact that the 
hind, not only at Upsala, but at several places along the 
oftiotlihiiLd, is grooved and striated pandlcl to the shoi 
often a( rii:lit angles to the markings of the ice fro 
inteii,ir. showing that the present bed of tho Baltic wi 
liirge t-n.'iigh to contain the iey stream. For example, 
the slum-t between Katniav and Kurlskrona, as described 
li.xlfriek Mimlusoii luul by M. Horbye, the striatioi 
IMVallel to ilie sh.'ie. I'erhaps the slight obstruction y 
by the isl.md of (M.i;i.l, vliuaied so elow to the shore, 
delKvt the rtlgx- oi' il'.e ^tivani at this pinnt over on thi 
The ie\ sin-oiu. ait.r jasMii^ Karlskrena, bent round 
*,-*t .ilorg the p'.vt^e;: en:r,i"iv :o l':;e Baltic, and 



h8 clima te and time. 

Again, that the ice, after passing down the Baltic, turned t 
the right along the southern end of Gothland, is shown by th 
direction of the stria) and ice-groovings observed on sucl 
islands as Gotlilaiid, Olaud, and Bomholm. Sir R. Murchisoi 
found that tlie island of Gothland is grooved and striated i 
one uniform direction from N.E. to S. W. " These groo^angs,' 
says Sir Roderick, " so perfectly resemble the flutings and strii 
produced in the Alps by the actual movement of glaciers, tha 
neitlicr M. Agassiz nor any one of his supporters could detect i 
difference." He concludes, however, that the markings couli 
not have been made by land-ice, because Gothland is not onl; 
a low, flat island in the middle of the Baltic, but is " at leas 
400 miles distant from any elevation to which the term o 
mountain can bo applied." This, of course, is conclusiv 
against the hypolhosis that Gothland and the other islands o 
the Baltic could have boon glaciated by ordinary glaciers ; bu 
it is quite in harmony with the theory that the Gulf of Botlmi; 
and the entire Baltic were filled with one continuous mass o 
lind-ice, derived from the drainage of the greater part o 
Sweden, Lapland, and Finland. In fact, the whole glacia 
phononiona of Scandinavia arc inexplicable on the hypothesi 
of local gLicicrs. 

That the Baltic was completely filled by a mass of ice moviii| 
from the north is further evidenced bv the fact that the main 
land, not only at Upsala, but at several places along the coas 
of Gothland, is grooved and striated parallel to the shore, am 
often at right angles to the markings of the ice from th 
interior, showing that the present bed of the Baltic was uu 
large enough to contain the icy stream. For example, aluui 
the shores bc^tween Kalmar and Karlskrona, as described bv Si 
Boderick Murchison and bv M. Ilorbve, the striations ar 
parallel to the shore. Perhaps the slight obstruction oilere 

• a 

by the island of Oland, situated so close to the shore, woul 
deflect the edge of the .stream at this point over on the lane 
The icy stream, after ])a8sing Karlskrona, bent round to th 
west along the present entrance to the Baltic, and agai 



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ICE'SHEET IN NORTH- WESTERN EUROPE. 449 

inyaded the mainland, and crossed over the low headland of 
Christianstadt, and thence passed westward in the direction of 
Zealand. 

This immense Baltic glacier would in all probability pass 
over Denmark, and enter the North Sea somewhere to the 
north of the Eiver Elbe, and would then have to find an outlet 
to the Atlantic through the English Channel, or pass in 
between our eastern shores and the mass from Gothland and 
the north-western shores of Europe. The entire probable path 
of the ice may be seen by a reference to the accompanying 
chart (Plate V.) That the ice crossed over Denmark is evident 
from the fact that the surface of that country is strewn with 
debris derived from the Scandinavian peninsiJa. 

Taking all these various considerations into account, the con- 
clusion is inevitable that the great masses of ice from Scotland 
would bo obliged to turn abruptly to the north, as represented 
in the diagram, and pass round into the Atlantic in the direc- 
tion of Caithness and tho Orknev Islands. 

If the foregoing be a fair representation of the state of 
matters, it is physically impossible that Caithness coxdd have 
escaped being overridden by the land-ice of the North Sea, 
Caithness, as is well known, is not only a low, flat tract of land, 
little elevated above the sea-level, and consequently incapable 
of supporting large glaciers; but, in addition, it projects in the 
form of a headland across the very path of the ice. Unless 
Caithness could have protected itself by pushing into tho sea 
glaciers of one or two thousand feet in thickness, it could not 
possibly have escaped the inroads of the ice of the North Sea. 
But Caithness itself could not have supported glaciers of this 
magnitude, neither could it have derived them from the adjoin- 
ing mountainous regions of Sutherland, for the ice of this coimty 
found a more direct outlet than along the flat plains of Caith- 
ness. 

The shells which the boulder clay of Caithness contains have 
thus evidently been pushed out of the bed of the North Sea by 
the land-ice, which formed the clay itself. 



UO CLIMATE AND TIME. 

The fact that these shells are not so intenaely arctio as thou 
found in Rome other quarters of Scotland, is no eiidence thai 
the clay was not fomiod during the most severe part of the 
glacial epoch, for the shells did not live in the North Sea at the 
time that it was filled with land-ice. The shells must hayc 
belonged to a period prior to the invasion of the ice, and con- 
sequently before the cold had reached its greatest intensity. 
Neither is there any necessity for supposing the shells to be 
pre-glacial, for these shells may have belonged to an inter- 
glacial period. In so far as Scotland is concerned, it would be 
hazardous to conclude that a plant or an animal is either pre- 
glacial or post-glacial simply because it may happen not to be 
of an arctic or of a boreal type. 

The same remarks which apply to Caithness apply to a 
certain extent to the headland at Fraserburgh. It, too, lay in 
the path of the ice, and from the direction of the striae on the 
rocks, and the presence of shells in the clay, as described by 
Mr. Jamieson, it bears evidence also of having been overridden 
bj' the land -ice of the Xorth Sea. In fact, we have, in the 
invasion of Caithness and the headland at Fraserburgh by the 
land- ice of the North Sea, a repetition of what we have seen 
took place at Upsula, Kalraar, Christianstadt, and other flat 
tracts along the sides of the Baltic. 

The scarcity, or perhaps entire absence of Scandinarvian 
boulders in the Caithness clay is not in any way unfavourable 
to the theory, for it would only be the loft edge of the North 
Sea glacier that could possibly pass over Caithness ; and thifi 
edge, as we have seen, w-as composed of the land-ice from Scot- 
land. We might expect, however, to find Scandinavian blocke 
on the Shetland and Faroe Islands, for, as we shall presently 
see, there is pretty good evidence to prove thnt the Scandinavian 
ice passed over these islands. 

The iShctland and Faroe Islands glaciated by Land-ice, — It is 
also worthy of notice that the striae on the rocks in the Orkney, 
Shetland, and Faroe Islands, all point in the direction of Scan- 
dinavia, and are what would be eflfected by land-ice moving in 



ICE-SHEET IN NORTH- WESTERN EUROPE. 431 

the paths indicated in the diagram. And it is a fact of some 
significance, that when we piroceed north to loelandy the striaD, 
according to the observations of Robert Chambers, seem to 
point towards North (Greenland. Is it possible that the entiiv 
Atlantic, from Scandinavia to Ghreenland, was filled with land* 
ice P Astoimding as this may at first appear, there are seyeral 
considerations which render such a conclusion probable. The 
observations of Chambers, Peach, Hibbert, Allan, and others, 
show that the rocky face of the Shetland and Faroe Islands has 
been ground, polished, and striated in a most remarkaUe 
manner. That this could not have been done by ice belonging 
to the islands themselves is obvious, for these islands are much 
too small to have supported glaciers of any size, and the 
smallest of them is striated as well as the lai^gest. Besides, 
the uniform direction of the striss on the rocks shows that it 
must have been efiected by ice passing over the islands. That 
the striations could not have been effected by floating icebergs at 
a time when the islands were submerged is, I think, equally 
obvious, from the fact that not only are the tops of the highest 
eminences ice-worn, but the entire surface down to the present 
sea*level is smoothed and striated ; and these striations conform 
to all the irregularities of the surfieu^. This last &ct Professor 
Geikie has clearly shown is wholly irreooncilable with the 
floating-ice theory.* Mr. Peach f found vertical precipices in 
the Shetlands grooved and striated, and the same thing was 
observed by Mr. Thomas Allan on the Faroe Islands, t That 
the whole of these islands have been glaciated by a continuoos 
sheet of ice passing over them was the impression left on the 
mind of Eobert Chambers after visiting them. S This is the 
theory which alone explains all the &cts. The only difficulty 
which besets it is the enormous thickness of the ice demanded 
by the theory. But this difficulty is very much diminished 

« <* Glacial Dnft of Scotland/' p. 29. 

t Qeological Magazine, vol. iL, p. 348. Brit Aiioo. Bep., 1S04 (Metioas), 
p 69. 
t Trans. Boy. Soc Edin., toI. vii., p. SS6. 
f ** Tiacings of Iceland and the Faroe Jalaudi,** f. 49. 



45* CLIMATE AND TIME. 

wHen we reflect that we have good evidenoey from, the tliiokxu 
of icebergs which have been met with in the Southern Oceaz 
that the ice moving off the antarctic continent must be in soi 
places considerably over a mile in thickness. It is then not 
surprising that the ice of the glacial epoch, coming off Gree 
land and Northern Europe, should not have been able to flo 
in the North Atlantic. 

Why tlie Ice of Scotland tens of such enormous Thick fu*s8.- 
The enormous thickness of the ice in Scotland, during tl 
glacial epoch, has been a matter of no little surprise. It 
remarkable how an island, not more than 100 miles acroe 
should have been covered with a sheet of ice so thick as to bui 
moxmtain ranges more than 1,000 feet in height, situated almo 
at the sea-shore. But all our difficulties disappear when v 
reflect that the seas around Scotland, o^ig to their shallow 
ness, were, during the glacial period, blocked up with solid ic 
Scotland, Scandinavia, and the North Sea, would form oi 
immense table-land of ice, from 1,000 to 2,000 feet above tl 
sea-level. This table-land would terminate in the deep wate; 
of the Atlantic by a perpendicular wall of ice, extending pn 
bably from the west of Ireland away in the direction of Icelani 
From this barri(T iceber«^s would be continually breaking ol 
rivalling in magnitude those which arc now to be met with i 
the antarctic seas. 

The great Ewtension of the Loess aeeounted for, — An effei 
which would result from the blocking up of the North Sea wit 
land-ice, would be that the waters of the Rhine, Elbe, an 
Thames would have to find an outlet into the Atlantic throng 
the English Channel. Professor Geikie has suggested to ni 
that if the Straits of Dover were not then open — cjuite a possib] 
thing — or were they blocked up with land-ice, say by the grer 
Baltic glacier crossing over from Denmark, the consequenc 
would l)e that the waters of the Rhine and Elbe would I 
dammed back, and would inundate all the low-lying tracts < 
3ountry to the south; and this might account for the extn 

• See Chap. XXII I. 



■I 




ICE'SHEET IN NORTH- WESTERN EUROPE. 453 

ordinary extension of the Loess in the basin of the Bhiue, and 
in Belgium and the north of France.* 

Note on the Olaciation of Caithness, . 

I have very lately received a remarkable confirmation of the 
path of the Caithness ice in observations communicated to me 
by Professor Geikio and Mr. B. N. Peach. The latter geolo- 
gist says, "Near the Ord of Caithness and on to Berriedale 
the striae pass off the land and out to sea ; but near Dunbeath, 
6 miles north-east of Berriedale, they begin to creep up out of 
the sea on to the land and range from about 15° to 10° 
east of north. Where the strice pass oat to the sea the boulder 
clay is made up of the materials from inland and contains no 
shells, but immediately the strice begin to creep up on to the land 
then shells begin to make their appearauce ; and there is a differ- 
ence, moreover, in the colour of the clay, for in the former 
case it is red and incoherent, and in the latter hard and dark- 
coloured." The accompanying chart (Plate VI.) shows the 
outline of the Caithness coast and the direction of the striae as 
observed by Professor Geikie and Mr. Peach, and no demon- 
stration could be more conclusive as to the path of the ice and 
the obstacles it met than these observations, supplemented and 
confirmed as they are by other recorded facts to which I shall 
presently allude. Had the ice-current as it entered the North 
Sea off the Sutherland coast met with no obstacle it would have 
ploughed its way outwards till it broke off in glaciers and 
rtoated away. But it is clear that the great press of Scandi- 
navian ice and the smaller mass of land-ice from the Moray- 
shire coast converging in the North Sea filled up its entire bed, 
and these, meeting the opposing current from the Sutherland 
coast, turned it back upon itself, and forced it over the north- 

* Mr. Thomas Belt has suhsoquently advanrcd (Quart. Jour. Geol. Soc, vol. 
SLXX., p. 490), a similrtr <;xpluiiation of the steppes of Siberia. He supposes that 
an overflow of ice from the p<3lar basin dammed back all the rivers flowing north- 
ward, and formed an immense lake which extended over the lowlands of Siberia, 
und deposited the ar^Bt beds of sand and silt wiih occasional fresh-water sheila 
and elephant remains, of which the stopp^s coniiit. 



) 



454 CLIMATE AND TIME. 

east part of Caithness. The farther south on the Satherlai 
coast that the ice entered the sea the deeper would it be ab 
t(f penetrate into the ocean-bed before it met an oppositk 
sufficiently strong to turn its course, and the wider would 1 
its sweep ; but when we come to the Sutherland coast we reac 
a point where the land-ice — as, for example, near Dunbeath — 
\ forced to bend round before it even reaches the sea-shore, i 

I will be seen from the accompanying diagram. 

We are led to the same conclusions regarding the path < 
the ice in the North Sea from the presence of oolitic fossils an 
I chalk flints found likewise in the boulder clay of Caithness, f( 

j these, as we shall see, evidently must have come from the se; 

' At the meeting of the British Association, Edinburgh, 1851 

Hugh Miller exhibited a collection of boreal shells with fra^ 
mcnts of oolitic fossils, chalk, and chjdk flints from the bouldt 
clay of Caithness collected by Mr. Dick, of Thurso. My frienc 
Mr. C. W. Peach, found that the chalk flints in the bouldt 
clay of Caithness become more abundant as we proceed nortl 
ward, while the island of Stroma in the Pentland Firth i 
found to be completely strewn with them. This same observe 
found, also, in the Caithness clay stones belonging to tl 
Oolitic and Lias formations, with their characteristic fossil; 
while ammonites, belemnitcs, fossil wood, &c., &c., were als 
found loose in the clay.* The explanation evidently is, tht 
these remains were derived from an outcrop of oolitic an 
cretaceous beds in the North Sea. It is well known that th 
eastern coast of Sutherlandshire is fringed with a narrow stri 
of oolite, which passes under the sea, but to what distance i 
not yet ascertained. Outside the Oolitic formation the chal 
beds in all probability crop out. It will be seen from a glauc 
at the accompanying chart (Phite VI.) that the ice which passe 
over the north-eastern part of Caithness must have crossed th 
out-cropping chalk beds. 

As has already been stated in the foregoing chapter, th 
headland of Fraserburgh, north-eastern comer of Aberdeen 

• Proc. Roy. Phys. Soc., Edin., vols. ii. and iiL 



ICE'SHEET IN NORTH- WESTERN EUROPE. 455 

shire, bears evidence, both from the direction of the striae and 
broken shells in the boulder clay, of having been overridden 
also by land- ice from the North Sea. This conclusion is 
strengthened by the fact that chalk flints and oolitic fossils have 
also been abundantly met with in the clay by Dr. Elnight, Mr. 
James Christie, Mr. W. Ferguson, Mr. I. F. Jamieson, and 
others. 



I NORTH OF EKOI^ND ICE-SHEET, AXD TRANSPORT OF W.lSTDAtB 
1 CBAQ 1 

P TnutRpoi 
I Ban 




CHAPTER XXVni. 



Tnuifiport of Block* ; Thaoriei of. 
;e probably ■triatod 



Mr.Looj' ... _ 

JDO.— Mr. Jnclt'a 8ngKe»lion— Shedding of Ic 
SnglsTid Ice-Rhrot.— Olnciation of Weot Bom< 
BO raru in Suulh of Ensland.— Furui ofConto] 

CoNsiiiERABi.K difficulty has bcon felt in